Introduce Polkadot-Sdk developer_hub (#2102)

This PR introduces the new crate `developer_hub` into the polkadot-sdk
repo. The vision for the developer-hub crate is detailed in [this
document](https://docs.google.com/document/d/1XLLkFNE8v8HLvZpI2rzsa8N2IN1FcKntc8q-Sc4xBAk/edit?usp=sharing).

<img width="1128" alt="Screenshot 2023-11-02 at 10 45 48"
src="https://github.com/paritytech/polkadot-sdk/assets/5588131/1e12b60f-fef5-42c4-8503-a3ba234077c3">


Other than adding the new crate, it also does the following: 

* Remove the `substrate` crate, as there is now a unique umbrella crate
for multiple things in `developer_hub::polkadot_sdk`.
* (backport candidate) A minor change to `frame-support` macros that
allows `T::RuntimeOrigin` to also be acceptable as the origin type.
* (backport candidate) A minor change to `frame-system` that allows us
to deposit events at genesis because now the real genesis config is
generated via wasm, and we can safely assume `cfg!(feature = "std")`
means only testing. related to #62.
* (backport candidate) Introduces a small `read_events_for_pallet` to
`frame_system` for easier event reading in tests.
* From https://github.com/paritytech/polkadot-sdk-docs/issues/31, it
takes action on improving the `pallet::call` docs.
* From https://github.com/paritytech/polkadot-sdk-docs/issues/31, it
takes action on improving the `UncheckedExtrinsic` docs.

## Way Forward

First, a version of this is deployed temporarily
[here](https://blog.kianenigma.nl/polkadot-sdk/developer_hub/index.html).
I will keep it up to date on a daily basis.

### This Pull Request

I see two ways forward: 

1. We acknowledge that everything in `developer-hub` is going to be WIP,
and merge this asap. We should not yet use links to this crate anywhere.
2. We make this be the feature branch, make PRs against this, and either
gradually backport it, or only merge to master once it is done.

I am personally in favor of option 1. If we stick to option 2, we need a
better way to deploy a staging version of this to gh-pages.

### Issue Tracking

The main issues related to the future of `developer_hub` are: 

- https://github.com/paritytech/polkadot-sdk-docs/issues/31
- https://github.com/paritytech/polkadot-sdk-docs/issues/4
- https://github.com/paritytech/polkadot-sdk-docs/issues/26 
- https://github.com/paritytech/polkadot-sdk-docs/issues/32
- https://github.com/paritytech/polkadot-sdk-docs/issues/36


### After This Pull Request

- [ ] create a redirect for
https://paritytech.github.io/polkadot-sdk/master/substrate/
- [x] analytics 
- [ ] link checker
- [ ] the matter of publishing, and how all of these relative links for
when we do, that is still an open question. There is section on this in
the landing page.
- [ ] updated https://paritytech.github.io/

---------

Co-authored-by: Liam Aharon <liam.aharon@hotmail.com>
Co-authored-by: Juan Girini <juangirini@gmail.com>
Co-authored-by: bader y <ibnbassem@gmail.com>
Co-authored-by: Sebastian Kunert <skunert49@gmail.com>
Co-authored-by: James Wilson <james@jsdw.me>
Co-authored-by: Michal Kucharczyk <1728078+michalkucharczyk@users.noreply.github.com>

docs/mermaid/IA.mmd

@@ -0,0 +1,14 @@
+flowchart
+    parity[paritytech.github.io] --> devhub[developer_hub]
+
+    devhub --> polkadot_sdk
+    devhub --> reference_docs
+    devhub --> tutorial
+
+    polkadot_sdk --> substrate
+    polkadot_sdk --> frame
+    polkadot_sdk --> cumulus
+    polkadot_sdk --> polkadot
+    polkadot_sdk --> xcm
+
+

docs/mermaid/extrinsics.mmd

@@ -0,0 +1,5 @@
+flowchart TD
+    E(Extrinsic) ---> I(Inherent);
+    E --> T(Transaction)
+    T --> ST("Signed (aka. Transaction)")
+    T --> UT(Unsigned)

docs/mermaid/polkadot_sdk_parachain.mmd

@@ -0,0 +1,11 @@
+flowchart LR
+	subgraph Parachain[A Polkadot Parachain]
+		ParachainNode[Parachain Node]
+		ParachainRuntime[Parachain Runtime]
+	end
+
+    FRAME -.-> ParachainRuntime
+    Substrate[Substrate Node Libraries] -.-> ParachainNoe
+
+    CumulusC[Cumulus Node Libraries] -.-> ParachainNode
+    CumulusR[Cumulus Runtime Libraries] -.-> ParachainRuntime

docs/mermaid/polkadot_sdk_polkadot.mmd

@@ -0,0 +1,10 @@
+flowchart LR
+
+	subgraph Polkadot[The Polkadot Relay Chain]
+		PolkadotNode[Polkadot Node]
+		PolkadotRuntime[Polkadot Runtime]
+	end
+
+    FRAME -.-> PolkadotRuntime
+    Substrate[Substrate Node Libraries] -.-> PolkadotNode
+

docs/mermaid/polkadot_sdk_substrate.mmd

@@ -0,0 +1,8 @@
+flowchart LR
+	subgraph SubstrateChain[A Substrate-based blockchain]
+		Node
+		Runtime
+	end
+
+    FRAME -.-> Runtime
+    Substrate[Substrate Node Libraries] -.-> Node

docs/mermaid/state.mmd

@@ -0,0 +1,16 @@
+flowchart TB
+    subgraph Node[Node's View Of The State 🙈]
+        direction LR
+        0x1234 --> 0x2345
+        0x3456 --> 0x4567
+        0x5678 --> 0x6789
+        :code --> code[wasm code]
+    end
+
+    subgraph Runtime[Runtime's View Of The State 🙉]
+        direction LR
+        ab[alice's balance] --> abv[known value]
+        bb[bob's balance] --> bbv[known value]
+        cb[charlie's balance] --> cbv[known value]
+        c2[:code] --> c22[wasm code]
+    end

docs/mermaid/stf.mmd

@@ -0,0 +1,21 @@
+flowchart LR
+    %%{init: {'flowchart' : {'curve' : 'linear'}}}%%
+    subgraph BData[Blockchain Database]
+        direction LR
+        BN[Block N] -.-> BN1[Block N+1]
+    end
+
+    subgraph SData[State Database]
+        direction LR
+        SN[State N] -.-> SN1[State N+1] -.-> SN2[State N+2]
+    end
+
+    BN --> STFN[STF]
+    SN --> STFN[STF]
+    STFN[STF] --> SN1
+
+    BN1 --> STFN1[STF]
+    SN1 --> STFN1[STF]
+    STFN1[STF] --> SN2
+
+

docs/mermaid/stf_simple.mmd

@@ -0,0 +1,4 @@
+flowchart LR
+	B[Block] --> STF
+    S[State] --> STF
+    STF --> NS[New State]

docs/mermaid/substrate_client_runtime.mmd

@@ -1,10 +1,12 @@
 graph TB
 subgraph Substrate
 	direction LR
-	subgraph Client
+	subgraph Node
 	end
+
 	subgraph Runtime
 	end
-	Client --runtime-api--> Runtime
-	Runtime --host-functions--> Client
+
+	Node --runtime-api--> Runtime
+	Runtime --host-functions--> Node
 end

docs/mermaid/substrate_dev.mmd

@@ -0,0 +1,2 @@
+flowchart LR
+	T[Using a Template] --> P[Writing Your Own FRAME-Based Pallet] --> C[Custom Node]

docs/mermaid/substrate_simple.mmd

@@ -1,7 +1,7 @@
 graph TB
 subgraph Substrate
 	direction LR
-	subgraph Client
+	subgraph Node
 	end
 	subgraph Runtime
 	end

docs/mermaid/substrate_with_frame.mmd

@@ -1,7 +1,7 @@
 graph TB
 subgraph Substrate
 	direction LR
-	subgraph Client
+	subgraph Node
 		Database
 		Networking
 		Consensus
@@ -15,6 +15,6 @@ subgraph Substrate
 			Identity
 		end
 	end
-	Client --runtime-api--> Runtime
-	Runtime --host-functions--> Client
+	Node --runtime-api--> Runtime
+	Runtime --host-functions--> Node
 end