Add submodule support to GitHub tag

On GitHub the submodule is only shown as a commit id.

I would like to know the tag (if any) associated with that tag.

eg:
https://img.shields.io/github/v/tag/:user:/:repo:/:submodule:

Would that be possible?

Start at the github/v/tag/:user:/:repo:/:submodule: endpoint described in the issue and trace how the current GitHub tag value is obtained. Check how submodule references are represented, then verify that a tag is returned when one is associated and that existing tag requests retain their behavior.

Written by the indexing model from the issue text.