Add `CheckMetadataHash` signed extension #807

Job	Run time
Build Runtimes (encointer-node-notee)	4m 39s
build-try-runtime-and-benchmarks	7m 30s
build	4m 26s
Cancel Previous Runs	2s
unit-tests	3m 40s
cargo-toml-fmt	8s
Rust check +nightly fmt --all -- --check (x86_64-unknown-linux-gnu)	52s
Rust check clippy -p encointer-client-notee (x86_64-unknown-linux-gnu)	3m 26s
test_bootstrap_demo_community.sh	21m 40s
test_bot_community.sh	9m 8s
test_register_business.sh	2m 19s
Draft Release	0s
Publish Runtimes	0s
	57m 50s

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