feat: ingest `signer_signature` from `/new_block` event and expose in new endpoint #2568

Job	Run time
test-2_5 (block-zero-handling)	1m 25s
test-2_5 (faucet-stx)	1m 22s
test-2_5 (pox-4-btc-address-formats)	2m 11s
test-2_5 (pox-4-delegate-aggregation)	2m 12s
test-2_5 (pox-4-delegate-stacking)	1m 51s
test-2_5 (pox-4-delegate-revoked-stacking)	2m 8s
test-2_5 (pox-4-stack-extend-increase)	2m 20s
lint	55s
test (api)	10m 8s
test-2_5 (pox-4-rosetta-btc-addr-types)	5m 38s
test-rosetta (rosetta)	3m 20s
test (bns)	3m 34s
test-2_5 (pox-4-rosetta-cycle-phases)	1m 16s
test-rosetta (rosetta-construction)	2m 19s
test-rosetta (rosetta-cli-data)	2m 14s
test-2_5 (pox-4-rosetta-segwit)	1m 41s
test-rosetta (rosetta-cli-construction)	3m 16s
test-2_5 (pox-4-burnchain-stack-stx)	1m 38s
test (bns-e2e)	7m 30s
test-2_5 (pox-4-burnchain-delegate-stx)	1m 43s
test (btc-faucet)	1m 34s
test (event-replay)	1m 58s
test (rpc)	1m 29s
build-publish	0s
	1h 3m 42s

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