Previous MR:
https://gitlab.com/gitlab-org/gitlab/-/merge_requests/29453

**Problem**

Current id contraint does not allow routes with `.` symbol.

* `gitlab-org/gitlab-shell/-/sse/master/CONTRIBUTING` - match
* `gitlab-org/gitlab-shell/-/sse/master/CONTRIBUTING.md` - 404 page

**Solution**

This MR restores the previous value for `id` constraint.

I've added a simple integration test to make sure that routing works
as expected.