Port of "API: Consolidate /projects endpoint" to EE

See merge request !1232

It consolidates these endpoints:
 - /projects
 - /projects/owned
 - /projects/visible
 - /projects/starred
 - /projects/all

Into the /projects endpoint using query parameters.

Backport "Move /projects/fork/:id to /projects/:id/fork"

See merge request !1228

Fix missing file extension for CHANGELOG entry

See merge request !1229

EE: Enable Style/RedundantException, Lint/EmptyWhen, and RSpec/ExpectActual cops

See merge request !1227

Backport "Remove deprecated templates endpoints in V4"

See merge request !1214

[EE] Resolve "GroupsController#activity.json is REALLY slow due to SQL"

See merge request !1226

CE upstream

Closes gitlab-com/gitlab-docs#68 and #1051

See merge request !1225

This is a little too picky, even for us.

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

Also, don't use limit in subquery, MySQL don't like that.
Signed-off-by: Rémy Coutable <remy@rymai.me>

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

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

# Conflicts:
#   app/models/repository.rb

[EE] Update Rubocop to Ruby 2.3

See merge request !1195

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

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

CE Upstream - Friday

Closes gitlab-ce#27955

See merge request !1218

Add member: Always return 409 when a member exists

See merge request !1215

Updated issue boards docs

Closes #27872

See merge request !9097

Add member: Always return 409 when a member exists

Closes #20732

See merge request !9093

removes grayish blue color for events activity

Closes #27608

See merge request !9179

Gather issuable  metadata to avoid n+ queries on index view

Closes #25900

See merge request !9006

The EE version of the protected branches JS doesn't take a label...

We should really reduce the disrepancies between CE and EE for this
feature.
Signed-off-by: Rémy Coutable <remy@rymai.me>

Update Rubocop to Ruby 2.3

See merge request !8994

Move merge requests index file inside the merge_requests dir

See merge request !9181

[ci skip]

Fix issue from milestone

See merge request !8895

Add method for creating foreign keys concurrently

See merge request !9069

Rename Files::DeleteService to Files::DestroyService

See merge request !9110

Resolve "Improve blockquote formatting in notification emails"

Closes #28029

See merge request !9157