commit_date: code cleanup and readme updates #6961

Job	Run time
context (workflow)	5s
tag-match (\d.\d.\d, 0)	6s
context (git)	3s
multi-images	6s
tag-schedule	5s
tag-match (\d.\d, 0)	11s
tag-schedule (cron-{{date 'YYYYMMDD'}})	6s
tag-match (v(.*), 1)	10s
tag-semver (auto)	5s
tag-schedule ({{date 'YYYYMMDD-HHmmss'}})	7s
tag-semver (true)	6s
tag-schedule (schedule)	5s
tag-semver (false)	10s
bake	19s
bake-annotations	29s
custom-labels-annotations	12s
docker-push	18s
flavor	9s
images	10s
global-exps	10s
json	10s
no-images	11s
output-env	25s
sep-tags ( )	6s
sep-tags (,)	11s
bake-cwd	17s
dump	33s
sha-short	11s
sha-short (16)	7s
	5m 23s

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