Use relative _path helper URLs in the GitLab UI -- EE merge edition

Closes gitlab-ce#40825

See merge request gitlab-org/gitlab-ee!3676

Resolve "GeoNodeStatus calculates numbers inefficiently"

Closes #3699

See merge request gitlab-org/gitlab-ee!3595

Add epic information to issue sidebar

Closes #3696

See merge request gitlab-org/gitlab-ee!3579

Integrated Browser Performance Testing

Closes #3046

See merge request gitlab-org/gitlab-ee!3507

Replace absolute URLs on related branches/MRs with relative url to avoid hostname -- EE merge edition

See merge request gitlab-org/gitlab-ee!3626

Add system notes for issue - epic association

Closes #3947

See merge request gitlab-org/gitlab-ee!3674

Improve geo docs based on geo demo on Dec 5

Closes #4138

See merge request gitlab-org/gitlab-ee!3648

Empty repo ee

See merge request gitlab-org/gitlab-ee!3673

GeoNode#projects now returns restricted/unrestricted projects relation and only when it's really needed should be plucked to an array.

Enhancements for Geo admin screen

Closes #3195

See merge request gitlab-org/gitlab-ee!3545

Docs: add EEU tier to the landing page

See merge request gitlab-org/gitlab-ee!3677