Add support for "Sponsor" button

Release notes

Gitlab allows project maintainers to displaying a Sponsor button in their repository.

Problem to solve

Open source development takes time. In order to be sustainable, funding is an important aspect. Making it more easily accessible to users is the goal of this feature request.

Proposal

Add the possibility to display a Sponsor button in the repository by adding a file called FUNDING.yml either to the root or to the .gitlab folder similar to what Github is providing (preferably with the same syntax).

Intended users

End-user using and supporting development of open source applications.

Feature Usage Metrics

Number of projects using this feature and number of clicks on that button.