Modify the `container_push()` rule to add an attribute `marker_tag`. The attribute will be optional. The `marker_tag` attribute will take the name of a tag. This will be in addition to the tag passed in the `tag` attribute. When `marker_tag` is specificed, the following needs to happen: 1. When pushing the image, the `marker_tag` is added in addition to the `tag` to the container image. 2. Change behavior of `skip_unchaged_digest`, when it is set to is `true`: **Current Behavior** Currently the rule checks the docker repo for a matching image given the sha of the current image. if there is a matching image present, the rule ignores pushing. [Code](https://github.com/bazelbuild/rules_docker/pull/1112/files?diff=split&w=1#diff-e7ac9e82a8d04eaeb4e5aad9adcfd47b1be9ecc3f7ee654e9c1717898842900b) **New Behavior** If a matching image is found in docker repo, check image tag. If image tag == `marker_tag` then ignore pushing, else push anyway (cause its not the latest image) ### Subtasks: - [ ] add `marker_tag` optional attribute - [ ] add `marker_tag` while pushing - [ ] change behavior of `skip_unchaged_digest`