feat(workflow): add digest-bearing image publication workflows #29

Job	Run time
sailr-workflow (ci-build-push-plan)	2m 57s
sailr-workflow (ci-generate)	2m 23s
sailr-workflow (ci-deploy-plan)	3m 1s
sailr-workflow (ci)	2m 37s
sailr-workflow (ci-build-plan)	2m 36s
sailr-ci-build	0s
staging-deploy	0s
	13m 34s

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