Badge request: GitHub last commit to any branch

:clipboard: **Description**
A badge for github which show the time for the last commit to any branch.

This is what I expected that the "GitHub last commit" badge would do, but it only checks the master branch.

:link: **Data**
I would hope that there is a similar solution as the already existing github badges, but I have no experience in querying github for such data.

:microphone: **Motivation**

For some projects the master branch will only update when there is a new release, which might be much more infrequent than any commits.
I found out that this badge was not really existing when I wanted a "last commit" badge and a "last release" badge. For my repo I can create the "last release" badge for my repo by pointing the current "last commit" badge to the master branch and using a custom label.
Similarly, it's possible to get the last commit to any specific branch, but not the last commit to the repo as a whole.

Review the existing GitHub badge implementations and their data source first, then determine how GitHub exposes the latest commit across any branch. The work is done when a badge can report the repository-wide latest commit while existing branch-specific and master-branch badges continue to work.

Written by the indexing model from the issue text.