Implement CheckMetadataHash extension (#4274)

This implements the `CheckMetadataHash` extension as described in
[RFC78](https://polkadot-fellows.github.io/RFCs/approved/0078-merkleized-metadata.html).

Besides the signed extension, the `substrate-wasm-builder` is extended
to support generating the metadata-hash.

Closes: #291

---------

Co-authored-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>
Co-authored-by: joe petrowski <25483142+joepetrowski@users.noreply.github.com>
Co-authored-by: Liam Aharon <liam.aharon@hotmail.com>
Co-authored-by: Kian Paimani <5588131+kianenigma@users.noreply.github.com>

.gitlab/pipeline/test.yml

@@ -417,6 +417,17 @@ check-tracing:
     - time cargo test --locked --manifest-path ./substrate/primitives/tracing/Cargo.toml --no-default-features
     - time cargo test --locked --manifest-path ./substrate/primitives/tracing/Cargo.toml --no-default-features --features=with-tracing
 
+# Check that `westend-runtime` compiles with the `metadata-hash` feature enabled.
+check-metadata-hash:
+  stage: test
+  extends:
+    - .docker-env
+    - .common-refs
+    - .run-immediately
+    - .pipeline-stopper-artifacts
+  script:
+    - time cargo build --locked -p westend-runtime --features metadata-hash
+
 # more information about this job can be found here:
 # https://github.com/paritytech/substrate/pull/3778
 test-full-crypto-feature: