Add `CheckMetadataHash` signed extension #802

Job	Run time
build-try-runtime-and-benchmarks	14m 18s
Cancel Previous Runs	2s
build	14m 16s
Build Runtimes (encointer-node-notee)	10m 54s
cargo-toml-fmt	8s
Rust check +nightly fmt --all -- --check (x86_64-unknown-linux-gnu)	45s
unit-tests	14m 20s
Rust check clippy -p encointer-client-notee (x86_64-unknown-linux-gnu)	1m 7s
${{ matrix.test }}	1s
Draft Release	1s
Publish Runtimes	1s
	55m 53s

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