refactor: move middlewares to corresponding packages (!585) · Merge requests · GitLab.org / gitlab-pages

What does this MR do?

Also HeaderMap is deprecated and it's been replaced with responde#Header

I added the Changelog trailer (e.g. Changelog: feature) to the commits that need to be included in the changelog
I added unit tests or they are not required
I added acceptance tests or they are not required
I added documentation (or it's not required)
I followed code review guidelines
I followed Go Style guidelines