Add Experimental Endorsement Signalling #16123

Job	Run time
check commits	8m 25s
lint code	3m 59s
cross compilation	32m 15s
sample configuration check	4m 59s
RPC and mobile compilation check	2m 7s
Sqlc check	2m 48s
check pinned dependencies (google.golang.org/grpc v1.59.0)	4s
run unit tests (btcd unit-cover)	17m 12s
run unit tests (unit tags="kvdb_etcd")	19m 14s
run macOS itest	33m 34s
run unit tests (unit tags="kvdb_postgres")	18m 37s
check pinned dependencies (github.com/golang/protobuf v1.5.3)	3s
run unit tests (unit tags="kvdb_sqlite")	17m 31s
check release notes updated	5s
run unit tests (btcd unit-race)	36m 9s
run unit tests (unit-module)	1m 0s
run ubuntu itests (btcd, backend=btcd cover=1)	21m 55s
run ubuntu itests (bitcoind, backend=bitcoind cover=1)	29m 23s
run windows itest	5m 31s
run ubuntu itests (bitcoind-notxindex, backend="bitcoind notxindex")	29m 4s
run ubuntu itests (bitcoind-rpcpolling, backend="bitcoind rpcpolling" cover=1)	30m 38s
run ubuntu itests (bitcoind-etcd, backend=bitcoind dbbackend=etcd)	41m 17s
run ubuntu itests (bitcoind-postgres, backend=bitcoind dbbackend=postgres)	51m 49s
run ubuntu itests (bitcoind-sqlite, backend=bitcoind dbbackend=sqlite)	31m 5s
run ubuntu itests (bitcoind-postgres-nativesql, backend=bitcoind dbbackend=postgres nativesql=true)	51m 39s
run ubuntu itests (bitcoind-sqlite-nativesql, backend=bitcoind dbbackend=sqlite nativesql=true)	31m 10s
run ubuntu itests (neutrino, backend=neutrino cover=1)	25m 38s
finish	5s
	9h 7m 16s

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