Fix API issues sorting

## What does this MR do?

Fix the sorting of issues in the API.

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

Instead of removing the '_at' suffix manually, we could add those versions to the `Sortable` concern instead.

## Why was this MR needed?

There were a couple of bugs:

* The global and project-specific issues endpoints wouldn't sort at all.
* Group sorting would work, but only if you applied two undocumented workarounds:
  * Always pass both `order_by` and `sort` (both are optional, so only one should be needed to change ordering).
  * Instead of passing `created_at` or `updated_at`, you needed to pass `created` or `updated`.

This makes the API implementation match the docs.

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [x] API support added
- Tests
  - [x] Added for this feature/bug
  - [ ] All builds are passing
- [x] Conform by the [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html)
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

## What are the relevant issue numbers?

Closes https://gitlab.com/gitlab-org/gitlab-ee/issues/983.

See merge request !6281

Add notification_settings API calls

## What does this MR do?
It adds API calls to get/update notification settings, globally and at the group/project level.

## Are there points in the code the reviewer needs to double check?
None

## Why was this MR needed?
Notification settings were updated, but related API calls were never created.

## What are the relevant issue numbers?
gitlab-org/gitlab-ce#19359

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [x] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [x] API support added
- Tests
  - [x] Added for this feature/bug
  - [x] All builds are passing
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

Closes #19359

See merge request !5632

Improve PipelinesFinder spec so that it does not depend on hard-coded database IDs

Fixes failed builds such as https://gitlab.com/gitlab-org/gitlab-ce/builds/3919501

See merge request !6291

Fixes failed builds such as https://gitlab.com/gitlab-org/gitlab-ce/builds/3919501

Restrict ldap return attributes

## What does this MR do?

Fixes the CE part of #13821. We really only ever need uid, dn, cn, and mail attributes, and in some cases, even less. This merge request strips the request down to those four attributes by default, and allows the caller to specify others, if needed. 

## Why was this MR needed?

This will improve performance especially in cases where the connection is slow between GitLab and LDAP, or when the LDAP object has lots of attributes we don't care about.

See merge request !6187

Pass the remember_me option into the u2f form and support it while authenticating

## What does this MR do?

Adds remember me support in the u2f authentication, and makes sure the flag gets passed from the login form to the u2f form.

Based on the changes for the same thing done for regular 2fa: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/4369

## Why was this MR needed?

The remember me option wasn't working for u2f devices (yubikey)

## What are the relevant issue numbers?

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/18103

See merge request !5918

Hides merge request button on branches page

## What does this MR do?

 If user does not have the correct permissions, the merge request button is hidden

## What are the relevant issue numbers?

Closes #21805

See merge request !6181

Use NotificationSetting::EMAIL_EVENTS for params

Avoid conflict with Admin labels when importing GitHub labels

If the GitHub project have duplicated labels from the Admin labels, the importer will use the Admin label.

Fixes #21319

See merge request !6158