Prefer `RSpec.describe` over `describe` in top-level namespace

Problem

The GitLab development docs were updated recently to prefer RSpec.describe over describe in top-level namespace. It is referenced here in the docs. This is a best practice to avoid a monkey patch and will be removed in RSpec 4.0.

References:

• gitlab#220018 (closed)
• gitlab#220218 (closed)

Proposal

We should update all specs to use RSpec.describe at the root level and disable the monkey patching going forward. See this issue for more information for how this was accomplished in GL.