Customize format for GitHub release date badge

:clipboard: **Description**

Currently it basically only shows `month`, and `month year` when it's not the running year.

I highly like to see a `YYYY-MM-DD` option for example, or even make that the default as that seems most natural and useful. Like the badge itself states it's a release **date**, not a release **month** or rough release time frame. :)

Could this be a parameter? `format=iso`

Linking #2744

Start by locating the GitHub release date badge implementation and the code that parses badge parameters. Check how the current month and year output is selected, then determine how an ISO date option should be represented and documented. Done means the requested format is supported without changing existing behavior, with relevant coverage for the new output.

Written by the indexing model from the issue text.