Export issues to CSV

Closes #1480

See merge request !1126

Geo: Don't load dependent models when fetching an existing GeoNode from the database

Closes #1827

See merge request !1348

Also fixed @issues_count in email after merge

[ci skip]

IssuableFinder#count_by_state called from cached_assigned_issuables_count with a string state was causing incorrect values to be cached.
Improvements to wording and rubocop fixes.

Remove support for Git Annex

See merge request !1302

[ci skip]

[ci skip]

[ci skip]

[ci skip]

[ci skip]

[ci skip]

Introduce one additional thread into bin/elastic_repo_indexer

See merge request !1372

Avoids creating unnecessary arrays in Issuable#labels_hash
Uses cached issues count in CSV export modal

Resolve "Custom hook errors don't display in merge request widget"

Closes #1852

See merge request !1375

Multiple issue boards milestone

Closes #1587 and #1156

See merge request !1150

API routes referencing a specific issue should use the issue `iid`

See merge request !1325

Merge branch '26732-combine-deploy-keys-and-push-rules-and-mirror-repository-and-protect-branches-settings-pages-ee' into 'master'

Port of 26732-combine-deploy-keys-and-push-rules-and-mirror-repository-and-prote…

See merge request !1167

[EE] Prometheus monitoring

See merge request !1374

Remove unnecessary Vue usage

See merge request !1363

Also fixed naming of a test in the deploy_keys_presenter

Used collection on the deploy_keys/_index.html partial render calls,
also added delegate methods on the deploy_keys_presenter.rb

Fixed the repository_controller_spec.rb

Added specs for the deploy_keys_presenter and added a new method in the presenter
called #key_available?

Fixed some minor UX inconsistencies and added a concern to handle
redirection