add(rpc): Adds `getblockheader` RPC method (#8967) #2108

Job	Run time
Generate crates matrix	9s
Check crates matrix	3s
Build zebrad crate	37m 16s
Build zebra-utils crate	16m 52s
Build zebra-test crate	1m 27s
Build zebra-state crate	22m 20s
Build zebra-script crate	3m 10s
Build zebra-scan crate	25m 50s
Build zebra-rpc crate	35m 8s
Build zebra-node-services crate	3m 24s
Build zebra-network crate	6m 40s
Build zebra-grpc crate	14m 32s
Build zebra-consensus crate	17m 2s
Build zebra-chain crate	4m 46s
Build tower-fallback crate	58s
Build tower-batch-control crate	1m 17s
Open or update issues for building crates individually failures	0s
	3h 10m 54s

Provide feedback