[featuregate] Deprecate NewFlag in favor of RegisterFlags #15327

Job	Run time
govulncheck	35s
govulncheck	35s
setup-environment	16s
setup-environment	16s
test-coverage	6m 52s
test-coverage	3m 59s
unittest-matrix (~1.21.3)	4m 5s
unittest-matrix (~1.21.3)	4m 5s
unittest-matrix (~1.20.10)	3m 20s
unittest-matrix (~1.20.10)	3m 20s
checks	1m 53s
checks	1m 53s
cross-build-collector (darwin, amd64)	54s
cross-build-collector (darwin, amd64)	54s
cross-build-collector (darwin, arm64)	1m 9s
cross-build-collector (darwin, arm64)	1m 9s
lint	2m 52s
lint	2m 52s
cross-build-collector (linux, 386)	40s
cross-build-collector (linux, 386)	40s
cross-build-collector (linux, amd64)	51s
cross-build-collector (linux, amd64)	51s
cross-build-collector (linux, arm64)	59s
cross-build-collector (linux, arm64)	59s
cross-build-collector (linux, ppc64le)	40s
cross-build-collector (linux, ppc64le)	40s
cross-build-collector (linux, arm, 7)	34s
cross-build-collector (linux, arm, 7)	34s
cross-build-collector (linux, s390x)	1m 3s
cross-build-collector (linux, s390x)	1m 3s
cross-build-collector (windows, 386)	1m 9s
cross-build-collector (windows, 386)	1m 9s
cross-build-collector (windows, amd64)	39s
cross-build-collector (windows, amd64)	39s
unittest	1s
unittest	1s
	54m 11s

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