feat: add variable `commit_date` #6937

Job	Run time
multi-images	15s
tag-match (\d.\d.\d, 0)	8s
tag-match (\d.\d, 0)	6s
tag-schedule	8s
tag-match (v(.*), 1)	7s
custom-labels-annotations	8s
tag-schedule (cron-{{date 'YYYYMMDD'}})	11s
flavor	12s
tag-schedule ({{date 'YYYYMMDD-HHmmss'}})	11s
tag-schedule (schedule)	7s
global-exps	11s
images	9s
json	8s
tag-semver (auto)	16s
tag-semver (true)	11s
tag-semver (false)	6s
bake	27s
bake-annotations	27s
bake-cwd	18s
docker-push	31s
no-images	7s
output-env	15s
sep-tags ( )	6s
sep-tags (,)	8s
sha-short	11s
sha-short (16)	7s
	5m 11s

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