feat(workflow): add digest-bearing image publication workflows #30

Job	Run time
sailr-workflow (ci)	2m 44s
sailr-workflow (ci-deploy-plan)	2m 55s
sailr-workflow (ci-build-plan)	3m 0s
sailr-workflow (ci-build-push-plan)	3m 5s
sailr-workflow (ci-generate)	2m 48s
sailr-ci-build	0s
staging-deploy	0s
	14m 32s

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