feat: added "Remove Co-Maintainer status" link for comaintainers

This new link brings a co-maintainer to a confirmation page, where
they can submit a form to remove their comaintainer record from the
database.

It is only available for current co-maintainers of any particular
package, both from a GET and POST standpoint.

Closes #360

Signed-off-by: Kevin Morris <kevr@0cost.org>
2 jobs for comaint-self-removal in 2 minutes and 48 seconds (queued for 4 seconds)