Add Experimental Endorsement Signalling #16615

Job	Run time
lint code	4m 4s
check commits	8m 59s
cross compilation	32m 24s
check pinned dependencies (google.golang.org/grpc v1.59.0)	3s
run macOS itest	48m 39s
check pinned dependencies (github.com/golang/protobuf v1.5.3)	3s
check release notes updated	6s
RPC and mobile compilation check	2m 16s
sample configuration check	1m 13s
Sqlc check	2m 55s
run ubuntu itests (btcd, backend=btcd cover=1)	31m 8s
run ubuntu itests (bitcoind, backend=bitcoind cover=1)	39m 13s
run unit tests (btcd unit-cover)	16m 40s
run windows itest	5m 39s
run ubuntu itests (bitcoind-notxindex, backend="bitcoind notxindex")	38m 57s
run unit tests (unit tags="kvdb_etcd")	18m 27s
run ubuntu itests (bitcoind-rpcpolling, backend="bitcoind rpcpolling" cover=1)	40m 32s
run unit tests (unit tags="kvdb_postgres")	17m 18s
run ubuntu itests (bitcoind-etcd, backend=bitcoind dbbackend=etcd)	53m 44s
run unit tests (unit tags="kvdb_sqlite")	16m 35s
run ubuntu itests (bitcoind-postgres, backend=bitcoind dbbackend=postgres)	1h 11m 36s
run unit tests (btcd unit-race)	35m 19s
run ubuntu itests (bitcoind-sqlite, backend=bitcoind dbbackend=sqlite)	41m 57s
run unit tests (unit-module)	2m 3s
run ubuntu itests (bitcoind-postgres-nativesql, backend=bitcoind dbbackend=postgres nativesql=true)	1h 11m 9s
run ubuntu itests (bitcoind-sqlite-nativesql, backend=bitcoind dbbackend=sqlite nativesql=true)	42m 0s
run ubuntu itests (neutrino, backend=neutrino cover=1)	37m 51s
finish	6s
	11h 20m 56s

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