Add check runtimes GH Workflow (#2252)

This PR introduces:
- a new script 
- a new GH Workflow 
- runtime reference spec files for `rococo` and `westend`

It brings a mechanism to check that part(s) of the runtimes' metadata
that should not change over time, actually did not change over time.

Ideally, the GHW should trigger when a release is edited but GH seem to
[have an issue](https://github.com/orgs/community/discussions/47794)
that prevents the trigger from working. This is why the check has been
implemented as `workflow_dispatch` for a start.

The `workflow_dispatch` requires a `release_id` that can be found using:
```
curl -s -H "Authorization: Bearer ${GITHUB_TOKEN}" \
   https://api.github.com/repos/paritytech/polkadot-sdk/releases | \
   jq '.[] | { name: .name, id: .id }'
```
as documented in the workflow.

A sample run can be seen
[here](https://github.com/chevdor/polkadot-sdk/actions/runs/6811176342).

.github/scripts/common/lib.sh

@@ -202,21 +202,26 @@ fetch_release_artifacts() {
   echo "Release ID : $RELEASE_ID"
   echo "Repo       : $REPO"
   echo "Binary     : $BINARY"
+  OUTPUT_DIR=${OUTPUT_DIR:-"./release-artifacts/${BINARY}"}
+  echo "OUTPUT_DIR : $OUTPUT_DIR"
 
+  echo "Fetching release info..."
   curl -L -s \
     -H "Accept: application/vnd.github+json" \
     -H "Authorization: Bearer ${GITHUB_TOKEN}" \
     -H "X-GitHub-Api-Version: 2022-11-28" \
     https://api.github.com/repos/${REPO}/releases/${RELEASE_ID} > release.json
 
-  # Get Asset ids
+  echo "Extract asset ids..."
   ids=($(jq -r '.assets[].id' < release.json ))
+  echo "Extract asset count..."
   count=$(jq '.assets|length' < release.json )
 
   # Fetch artifacts
-  mkdir -p "./release-artifacts/${BINARY}"
-  pushd "./release-artifacts/${BINARY}" > /dev/null
+  mkdir -p "$OUTPUT_DIR"
+  pushd "$OUTPUT_DIR" > /dev/null
 
+  echo "Fetching assets..."
   iter=1
   for id in "${ids[@]}"
   do