This reverts commit a431ca0f.

Currently, our procedure for adding a commit requires us to execute `CreateBranchService` before file creation.
It's OK, but also we do execute `git hooks` (the `PostReceive` sidekiq job) as part of this process.
However, this hook is execute before the file is actually committed, so the ref is updated.

Secondly, we do execute a `git hooks` after committing file and updating ref.
This results in duplicate `PostReceive` jobs, where the first one is completely invalid.

This change makes the branch creation, something that is intermediate step of bigger process (file creation or update, commit cherry pick or revert) to not execute git hooks.

Signed-off-by: NRémy Coutable <remy@rymai.me>

This reverts commit 530f5158.

See !4892.
Signed-off-by: NRémy Coutable <remy@rymai.me>

This reverts commit 9ca633eb, reversing
changes made to fb229bbf.

1. Don't use case statements for dispatch anymore. This leads to a lot
   of duplication, and makes the logic harder to follow.

2. Remove duplicated logic.

    - For example, the `can_push_to_branch?` exists, but we also have a
      different way of checking the same condition within `change_access_check`.

    - This kind of duplication is removed, and the `can_push_to_branch?`
      method is used in both places.

3. Move checks returning true/false to `UserAccess`.

    - All public methods in `GitAccess` now return an instance of
      `GitAccessStatus`. Previously, some methods would return
      true/false as well, which was confusing.

    - It makes sense for these kinds of checks to be at the level of a
      user, so the `UserAccess` class was repurposed for this. The prior
      `UserAccess.allowed?` classmethod is converted into an instance
      method.

    - All external uses of these checks have been migrated to use the
      `UserAccess` class

4. Move the "change_access_check" into a separate class.

    - Create the `GitAccess::ChangeAccessCheck` class to run these
      checks, which are quite substantial.

    - `ChangeAccessCheck` returns an instance of `GitAccessStatus` as
      well.

5. Break out the boolean logic in `ChangeAccessCheck` into `if/else`
   chains - this seems more readable.

6. I can understand that this might look like overkill for !4892, but I
   think this is a good opportunity to clean it up.

    - http://martinfowler.com/bliki/OpportunisticRefactoring.html

Rename ENV['PROTOCOL'] to ENV['GL_PROTOCOL'] to conform to what GitLab Shell expects and make the `protocol` param in `GitAccess` mandatory.

Issue: https://gitlab.com/gitlab-org/gitlab-ce/issues/12785
Merge Request: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/3514

* Now checking if a commit is already reverted or there is a conflict is
  much more faster.
* No longer need to create a new branch.