Add option to remote mirrors to only push protected branches

Closes #3843

See merge request gitlab-org/gitlab-ee!3350

Remove epic sidebar props that were added by bad merge conflict

Closes #4073

See merge request gitlab-org/gitlab-ee!3441

Move EE-only admin and group views to the top-level EE directory

See merge request gitlab-org/gitlab-ee!3457

Fix linking issues from subgroups to epics in parent group

Closes #4069

See merge request gitlab-org/gitlab-ee!3445

[EE] Adds Rubocop rule for line break after guard clause

See merge request gitlab-org/gitlab-ee!3409

Remove duplicate mixins

See merge request gitlab-org/gitlab-ee!3455

Resolve "Add docs for gitlab slack app setup"

Closes #4043

See merge request gitlab-org/gitlab-ee!3428

Add next step link to ssh authorization geo step

Closes #4089

See merge request gitlab-org/gitlab-ee!3459

Geo: Ensure that repository deletions are communicated to the secondary

See merge request gitlab-org/gitlab-ee!3440

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

Update docs for Canary monitoring - docs

See merge request gitlab-org/gitlab-ee!3438

# Conflicts:
#   db/schema.rb

(EE-port) Delete empty fork networks

See merge request gitlab-org/gitlab-ee!3451

CE Port: Add request rate limits

See merge request gitlab-org/gitlab-ee!3444

Update current geo limitations

See merge request gitlab-org/gitlab-ee!3454

Fix generated clone URLs for wikis on Geo secondaries

Closes #4054

See merge request gitlab-org/gitlab-ee!3448

Update service desk docs to say user doesn't count toward limit

See merge request gitlab-org/gitlab-ee!3430

Reduce the number of Elasticsearch client instances that are created

Closes #3650

See merge request gitlab-org/gitlab-ee!3432

Add allow remote mirrors to be setup for projects documentation.

See merge request gitlab-org/gitlab-ee!3425

CE Port: Performance issues when loading large number of wiki pages

See merge request gitlab-org/gitlab-ee!3420

When collecting instance profile credentials in AWS, each client instantiation
is a HTTP request to an external web service. This service may rate-limit us
if we perform too many requests in a given time period.

A typical GitLab deployment will have many processes running, and each of those
processes needs *one* elasticsearch client instance. The client instance is
thread-safe and handles concurrent requests very well, with HTTP keep-alive
connections.

Prior to this commit, each process using elasticsearch would instantiate one
client per *class* that used `Elasticsearch::Model::Client`. So a multi-node
setup might look like:

```
* Server A
  * Unicorn parent
    * Unicorn child A
      * Client for Project class
      * Client for Repository class
      * Client for Issue class
      * ...
    * Unicorn child B
      * Client for Project class
      * Client for Repository class
      * Client for Issue class
      * ...
  * Sidekiq
    * Client for Project class
    * Client for Repository class
    * Client for Issue class
    * ...
* Server B
  * Unicorn master
    * ... (same as above)
  * Sidekiq
    * .... (same as above)
```

(total: N, plus N per unicorn child, multipled by the number of servers)

Following this commit, we have the following clients instead:

```
* Server A
  * Sidekiq (1 client)
  * Unicorn parent
    * Unicorn child A (1 client)
    * Unicorn child b (1 client)
* Server B
  * ... (same as above)
```

(total: 1, + 1 per unicorn child, multipled by the number of servers)

This drastically reduces the number of HTTP connections we make to the
Elasticsearch and AWS instance profile credentials servers, and should
come with a small increase in performance due to better utilisation of
those connections.