Backports changes made in https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/5063 to CE

See merge request gitlab-org/gitlab-ce!17909

[Rails5] Add `Gemfile.rails5`

See merge request gitlab-org/gitlab-ce!17761

Issuable list: add tooltips to icons

Closes #43786

See merge request gitlab-org/gitlab-ce!17700

Fixes the web IDE link in tree list opening the wrong URL

Closes #44477

See merge request gitlab-org/gitlab-ce!17900

[Rails5] Update ar5_batching initializer

See merge request gitlab-org/gitlab-ce!17825

[Rails5] Update ar5_pg_10_support initializer

See merge request gitlab-org/gitlab-ce!17826

Remove parser warnings workaround

See merge request gitlab-org/gitlab-ce!17901

Send Gitaly payload for git-upload-archive SSH commands

Closes gitaly#1092

See merge request gitlab-org/gitlab-ce!17903

Add indexes for user activity queries.

Closes #44446

See merge request gitlab-org/gitlab-ce!17890

makes caret go to the right side when closing most right issueboard list

Closes #40913

See merge request gitlab-org/gitlab-ce!17773

Convenient use of concurrent migration helpers

Closes #43887

See merge request gitlab-org/gitlab-ce!17888

NestingDepth (level 5) in framework/dropdowns.scss

See merge request gitlab-org/gitlab-ce!17820

Updated in:
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/17673

Closes #44446.

Changes empty project avatar to identicon in the IDE

Closes #44298

See merge request gitlab-org/gitlab-ce!17899

Refactor ConfirmDangerModal into ES module

See merge request gitlab-org/gitlab-ce!17874

Closes #44477

Update licensee 8.7.0 -> 8.9

Closes #18077

See merge request gitlab-org/gitlab-ce!17719

Closes #44298

Update gettext_i18n_rails_js 1.2.0 -> 1.3

See merge request gitlab-org/gitlab-ce!17801

Move IDE to CE

Closes #44157

See merge request gitlab-org/gitlab-ce!17887

Strip any query string parameters from Location headers from lograge

See merge request gitlab-org/gitlab-ce!17895

Port of https://github.com/roidrage/lograge/pull/241

Add performance monitoring docs for the new FE guide

See merge request gitlab-org/gitlab-ce!17809

Update spec import path for vue mount component helper

See merge request gitlab-org/gitlab-ce!17880

Closes #43887.

Index creation does not have an effect if the index is present already.
Index removal does not have an affect if the index is not present.

This helps to avoid patterns like this in migrations:
```
if index_exists?(...)
  remove_concurrent_index(...)
end
```

Resolve "Loss of input text on comments after preview"

Closes #42880

See merge request gitlab-org/gitlab-ce!17076