Support branches as input for GET /projects/:id/languages

Proposal

Provide the ability to pass in a branch to GET /projects/:id/languages to get back the programming languages in use on that particular branch. https://docs.gitlab.com/ee/api/projects.html#languages

Our organization is looking to setup standards around programming language usage and if we wait until teams merge into the mainline (default) branch, our feedback loop is slower.

This issue is similar where other customers cannot see language break down by branch in the UI either - #25428