add link_to_if helper on target_branch link on Merge Request show page for case of deleted target branch

add spec on #24507 bug description

add changelog entry

fix changelog

remove unnecessary js:true from specs

change spec title

add test for link to target branch before deletions

renamed spec about state of target branch link before and after deletion

some fixes into spec

Update outdated visible content spec descriptions

This fixes some spec descriptions that were not fixed in https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/7947.

See merge request !7971

Fix Backup::Manager#remove_old

Closes #25399

See merge request !7972

Fix typos in API doc examples

## What does this MR do?

Fixes a typo in the API docs. The `curl` examples in [build_triggers.md](doc/api/build_triggers.md) and [build_variables.md](doc/api/build_variables.md) all have a typo in the auth header. They all say `PRIVATE_TOKEN` when it should be `PRIVATE-TOKEN`.

## What are the relevant issue numbers?
Fixes #24565

See merge request !7514

Run builds with runners with tags gitlab-org and 2gb

## What does this MR do?

Added `gitlab-org` and `2gb` tags for jobs in `.gitlab-ci.yml`. So builds will be picked up by `gitlab-shared-runners-manager-X.gitlab.com runners`

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

Only `.gitlab-ci.yml`

## Why was this MR needed?

https://gitlab.com/gitlab-com/infrastructure/issues/714

## Screenshots (if relevant)


## Does this MR meet the acceptance criteria?

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

## What are the relevant issue numbers?

https://gitlab.com/gitlab-com/infrastructure/issues/714

See merge request !7757

Grapify the issues API

Related to #22928

See merge request !7968

Update GLU index for new report, broken links + typos

## What does this MR do?
Update text on GLU documentation for spelling and new State of DevOps book. 

/cc @axil

See merge request !7962

Bump Git version requirement to 2.8.4

Following gitlab-org/omnibus-gitlab!1108, the install doc and README should be updated too.

See merge request !7878

Bump gitlab-shell version to 4.0.3

See merge request !7953

Move admin hooks spinach to RSpec

https://gitlab.com/gitlab-org/gitlab-ce/issues/23036

See merge request !7942

Move admin logs spinach test to RSpec

https://gitlab.com/gitlab-org/gitlab-ce/issues/23036

See merge request !7945

UX Guide - add initial animation guidance

Adding guidance to our UX Guide around animation. This is to help us implement #24831 and add polished, consistent animation throughout GitLab.

See merge request !7780

Use :maximum instead of :within for length validators with a 0..N range

Closes #25209

See merge request !7894

Update php.md - /.dockerinit was removed in v1.11 so the test always results in …

See merge request !7882

Add excoveralls in list of coverage examples

See merge request !7906

Update custom_hooks.md for chained hooks support

See merge request !6721

Fix 404 error when visit group label edit page

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/25158

See merge request !7957

Remove caching of Repository#has_visible_content?

This MR removes the caching of `Repository#has_visible_content?`. The cache for this method is no longer necessary and this should solve the problem described in https://gitlab.com/gitlab-org/gitlab-ce/issues/25278.

See merge request !7947

A simpler implementation of finding a merge request

## What does this MR do?

This cleans up some code in the issues API as discussed in https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/7180#note_19501743

The helper method `merge_request_for_resolving_discussions` was no longer needed as it was only used once. That made it possible to simplify the implementation.

## Does this MR meet the acceptance criteria?

- [x] ~~[Changelog entry](https://docs.gitlab.com/ce/development/changelog.html) 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
  - [ ] 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 it does - 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?

!7180

See merge request !7955

Remove more pages css

* Moves award emojis to `/framework`
* Moves generic image styles to `/framework`
* Removes `confirmation.scss`

See merge request !7952

correct heading level for topics
Update puppet dev ops report for 2016

Remove dashboard.scss

See merge request !7960

# Conflicts:
#   app/assets/stylesheets/framework.scss

Remove tags.scss

Remove `tags.scss`

See merge request !7935

Remove admin.scss

Removes admin-specific CSS

See merge request !7932

https://gitlab.com/gitlab-org/gitlab-shell/merge_requests/93

https://gitlab.com/gitlab-org/gitlab-ce/issues/23036

https://gitlab.com/gitlab-org/gitlab-ce/issues/23036

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Following a discussion in !7180

Encourage bug reporters to mention if they use GitLab.com [ci skip]

See merge request !7954

Explain "js: true" in "deleted_source_branch_spec.rb"

See merge request !7949