Add documentation around FRAME Origin (#3362)

Does the following: 

- Add a reference doc page named `frame_runtime_types`, which explains
what types like `RuntimeOrigin`, `RuntimeCall` etc are.
- On top of it, it adds a reference doc page called `frame_origin` which
explains a few important patterns that we use around origins
- And finally brushes up `#[frame::origin]` docs. 
- Updates the theme, sidebar and favicon to look like: 

<img width="1728" alt="Screenshot 2024-02-20 at 12 16 00"
src="https://github.com/paritytech/polkadot-sdk/assets/5588131/6d60a16b-2081-411b-8869-43b91920cca9">


All of this was inspired by
https://substrate.stackexchange.com/questions/10992/how-do-you-find-the-public-key-for-the-medium-spender-track-origin/10993

closes https://github.com/paritytech/polkadot-sdk-docs/issues/45
closes https://github.com/paritytech/polkadot-sdk-docs/issues/43
contributes / overlaps with
https://github.com/paritytech/polkadot-sdk/pull/2638 cc @liamaharon
deprecation companion:
https://github.com/substrate-developer-hub/substrate-docs/pull/2131
pba-content companion:
https://github.com/Polkadot-Blockchain-Academy/pba-content/pull/977

---------

Co-authored-by: Radha <86818441+DrW3RK@users.noreply.github.com>
Co-authored-by: Sebastian Kunert <skunert49@gmail.com>
Co-authored-by: Gonçalo Pestana <g6pestana@gmail.com>
Co-authored-by: Liam Aharon <liam.aharon@hotmail.com>

Cargo.lock

@@ -13384,11 +13384,20 @@ dependencies = [
  "cumulus-pallet-parachain-system",
  "docify",
  "frame",
+ "frame-system",
  "kitchensink-runtime",
  "pallet-aura",
+ "pallet-authorship",
+ "pallet-balances",
+ "pallet-collective",
  "pallet-default-config-example",
+ "pallet-democracy",
  "pallet-examples",
+ "pallet-multisig",
+ "pallet-proxy",
  "pallet-timestamp",
+ "pallet-transaction-payment",
+ "pallet-utility",
  "parity-scale-codec",
  "sc-cli",
  "sc-client-db",