Beat [4/4]: implement `Consumer` in `chainWatcher` #16958

Job	Run time
Sqlc check	1s
lint code	1s
RPC and mobile compilation check	1s
check commits	1s
cross compilation (i386, freebsd-386 linux-386 windows-386)	1s
sample configuration check	1s
cross compilation (amd64, darwin-amd64 freebsd-amd64 linux-amd64 netbsd-amd64 openbsd-amd64 windo...	1s
run unit tests (btcd unit-cover)	1s
cross compilation (arm, darwin-arm64 freebsd-arm linux-armv6 linux-armv7 linux-arm64 windows-arm)	1s
run unit tests (unit tags="kvdb_etcd")	1s
check pinned dependencies (google.golang.org/grpc v1.59.0)	1s
run unit tests (unit tags="kvdb_postgres")	1s
check pinned dependencies (github.com/golang/protobuf v1.5.3)	1s
run windows itest	0s
run unit tests (unit tags="kvdb_sqlite")	1s
run unit tests (btcd unit-race)	1s
run macOS itest	0s
run unit tests (unit-module)	1s
check release notes updated	1s
run ubuntu itests	0s
finish	3s
	20s

Provide feedback