[EE] Try to find the merge-base against the canonical master and name the remotes

See merge request gitlab-org/gitlab-ee!3493

Fix spec to ensure BaseSyncService doesn't leave deleted directory around

See merge request gitlab-org/gitlab-ee!3509

Merge alpha_database into database

Closes gitlab-org/build/team-tasks#62

See merge request gitlab-org/gitlab-ee!3511

As these instructions are now GA for 10.2, we move the contents of
alpha_database.md into database.md, as a new section `Configure using
Omnibus for High Availability`.  The old section heading is kept to
redirect the user to either the new guide, or the old version of the docs.

We move the architecture discussion up, to supplement the overview of
the install.

Also, name the remotes in Gitlab::EeCompatCheck
Signed-off-by: Rémy Coutable <remy@rymai.me>

Don't user issuable_sort cookie for epics collection

Closes #4114

See merge request gitlab-org/gitlab-ee!3502

Document a failure mode for large repositories in Geo

See merge request gitlab-org/gitlab-ee!3500

[ci skip]

[ci skip]

Remove read-only flash message on admin pages

See merge request gitlab-org/gitlab-ee!3495

Merge branch 'ee-39461-notes-api-for-issues-no-longer-returns-label-additions-removals' into 'master'

Port 15080 to EE

See merge request gitlab-org/gitlab-ee!3478

Resolve "Configurable issue boards should be part of GitLab.com early adopter plan"

Closes #4115 and gitlab-com/support-forum#2729

See merge request gitlab-org/gitlab-ee!3497

Add example of finding the repmgr node id

Closes gitlab-org/build/team-tasks#46

See merge request gitlab-org/gitlab-ee!3491

Add example output for `repmgr standby setup`

Closes gitlab-org/build/team-tasks#36

See merge request gitlab-org/gitlab-ee!3501

Move ee-only files under top level ee directory

See merge request gitlab-org/gitlab-ee!3498

Tell the user what to prepare

Closes gitlab-org/build/team-tasks#61

See merge request gitlab-org/gitlab-ee!3494

It's useful to have sample output for this command, as it's a few moving
parts.

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

Port from CE to EE: Changing OAuth lookup to be case insensitive

See merge request gitlab-org/gitlab-ee!3427

Update gitlab.yml.example to match the default settings for Geo sync workers

See merge request gitlab-org/gitlab-ee!3488

Copyedit Epics docs

Closes #4062

See merge request gitlab-org/gitlab-ee!3482

Rather than telling the user to read ahead to figure out what
information to prepare, tell them the variables we're going to make use
of, and link them back to where we described them.  This should help in
the case a user is skipping ahead.

Add notes about architecture to PG HA document

Closes omnibus-gitlab#2705

See merge request gitlab-org/gitlab-ee!3490