Tag globs for checks

[martinxsliu]

Hi all! I have a use case where I only want the Docker image resource to pick up new versions if the tag matches some glob pattern. For example, only pick up tags like foo:release-xxx and ignore other tags like foo:dev-xxx. This would be similar to the paths source config for the git resource (see here). Is this a feature that's been discussed earlier?

Looking at the check command, it seems that we're fetching the manifest for the tag to get the tag's latest digest. Implementation wise, in order to support tag globbing I think we'll need to add a call to first fetch all tags for the image, apply the globbing, then fetch the manifest as normal using the latest tag.