Docs new index for project's settings

See the general Documentation guidelines http://docs.gitlab.com/ce/development/doc_styleguide.html

What does this MR do?

Adds new doc index to project's settings.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/35719

Note: branch created from https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/13545's, which needs to be merged before this.

changed the description

Update: this MR was deprioritized, and I will be taken back as soon as I finish a few other higher priorities on my list.

added 1745 commits

• 78b90261...b5a06c60 - 1742 commits from branch master
• c48310c8 - Merge branch 'master' of gitlab.com:gitlab-org/gitlab-ce into docs-new-topic-projects-settings
• c42ad3ef - copyedit
• d9bb19fa - add screenshots

Compare with previous version

added 1 commit

• 9b63f7db - move default branches to /branches/index.md

Compare with previous version

@axil can you please review? :)

assigned to @axil

added docs-review and removed docs-write labels

mentioned in issue #37482

assigned to @marcia

resolved all discussions

added 4 commits

• 92d742a1 - index /branches/ from repository and project indexes
• 601cdf40 - add more meat to the branches doc
• 812bd3e1 - reorder items
• 72f6b188 - Axil's review

Compare with previous version

added 3 commits

• fcb95a50 - index /branches/ from CE/readme
• 2aa3eb43 - link other indexes from ce/readme
• d356c686 - copyedit

Compare with previous version

@axil, if you want to take a second look, otherwise, it should be good to go. :)

assigned to @JobV