Add nightly CI check against latest substrate. (#335)

* Add nightly check and use specific version (currently the same) in PR checks

* wrong var name, whoops

* Create GH issue if nightly run fails

* need tokio feature for RpcClient; match dependency in root Cargo.toml.

* Ensure substrate command is properly cleaned up in the event of a panic, to prevent blocking

* increase retry limit again

* fmt

* Tweak text for nightly-run-failed issue template

* Run nightly-CI every 5mins for testing

* I clearly dont use cron enough

* Put back cron timings to 8am daily

* break a test

* revert nightly workflow again (doesnt run off master) and testing rust workflow

* more testing..

* undo testing things; seems to work

* tidy up; substrate url at top of both CI files

.github/workflows/rust.yml

@@ -14,6 +14,8 @@ on:
 
 env:
   CARGO_TERM_COLOR: always
+  # TODO: Currently pointing at latest substrate; is there a suitable binary we can pin to here?
+  SUBSTRATE_URL: https://releases.parity.io/substrate/x86_64-debian:stretch/latest/substrate/substrate
 
 jobs:
   build:
@@ -25,7 +27,7 @@ jobs:
 
       - name: Download Substrate
         run: |
-            curl "https://releases.parity.io/substrate/x86_64-debian:stretch/latest/substrate/substrate" --output substrate --location
+            curl $SUBSTRATE_URL --output substrate --location
             chmod +x substrate
             mkdir -p ~/.local/bin
             mv substrate ~/.local/bin
@@ -79,7 +81,7 @@ jobs:
 
       - name: Download Substrate
         run: |
-            curl "https://releases.parity.io/substrate/x86_64-debian:stretch/latest/substrate/substrate" --output substrate --location
+            curl $SUBSTRATE_URL --output substrate --location
             chmod +x substrate
             mkdir -p ~/.local/bin
             mv substrate ~/.local/bin
@@ -95,7 +97,7 @@ jobs:
         uses: Swatinem/rust-cache@v1.3.0
 
       - name: Check internal documentation links
-        run: RUSTDOCFLAGS="--deny broken_intra_doc_links" cargo doc --verbose --workspace --no-deps --document-private-items
+        run: RUSTDOCFLAGS="--deny rustdoc::broken_intra_doc_links" cargo doc -vv --workspace --no-deps --document-private-items
 
   tests:
     name: Cargo test
@@ -106,7 +108,7 @@ jobs:
 
       - name: Download Substrate
         run: |
-            curl "https://releases.parity.io/substrate/x86_64-debian:stretch/latest/substrate/substrate" --output substrate --location
+            curl $SUBSTRATE_URL --output substrate --location
             chmod +x substrate
             mkdir -p ~/.local/bin
             mv substrate ~/.local/bin
@@ -136,7 +138,7 @@ jobs:
 
       - name: Download Substrate
         run: |
-            curl "https://releases.parity.io/substrate/x86_64-debian:stretch/latest/substrate/substrate" --output substrate --location
+            curl $SUBSTRATE_URL --output substrate --location
             chmod +x substrate
             mkdir -p ~/.local/bin
             mv substrate ~/.local/bin