Resolve "Asset was not declared to be precompiled in production, favicon-green.ico"

What does this MR do?

This should fix for good the "precompile" issues for EE assets that are now located under ee/assets.

Are there points in the code the reviewer needs to double check?

Why was this MR needed?

Because https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/4129 introduced failures in development.

Does this MR meet the acceptance criteria?

• Review
  • Has been reviewed by Backend
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together

What are the relevant issue numbers?

Closes #4666 (closed)