Support disabling `DOCKER_METADATA_OUTPUT_*` environment variables #7056

Job	Run time
bake-path-context	17s
bake	18s
bake-annotations	18s
context (workflow)	3s
custom-labels-annotations	6s
context (git)	20s
docker-push	29s
dump	1m 9s
flavor	6s
global-exps	30s
images	5s
multi-images	6s
no-images	6s
no-output-env	5s
json	6s
output-env	14s
sep-tags ( )	6s
sha-short	6s
sep-tags (,)	7s
tag-match (\d.\d.\d, 0)	6s
sha-short (16)	5s
tag-match (\d.\d, 0)	6s
tag-schedule	9s
tag-match (v(.*), 1)	28s
tag-schedule (cron-{{date 'YYYYMMDD'}})	44s
tag-semver (auto)	5s
tag-schedule ({{date 'YYYYMMDD-HHmmss'}})	44s
tag-semver (true)	6s
tag-semver (false)	4s
tag-schedule (schedule)	6s
	7m 20s

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