feat: allow images input to be empty to output bare tags #6396

Job	Run time
flavor	5s
labels	7s
multi-images	6s
images	8s
tag-match (\d.\d.\d, 0)	3s
tag-schedule	8s
tag-semver (auto)	3s
tag-match (\d.\d, 0)	4s
tag-schedule (cron-{{date 'YYYYMMDD'}})	4s
tag-match (v(.*), 1)	4s
tag-semver (true)	6s
tag-schedule ({{date 'YYYYMMDD-HHmmss'}})	5s
tag-semver (false)	5s
tag-schedule (schedule)	3s
bake	18s
bake-annotations	21s
docker-push	35s
global-exps	5s
no-images	4s
json	4s
output-env	10s
sep-tags ( )	3s
sep-tags (,)	3s
	2m 54s

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