Update DB migrations style guide: prefer atomic migrations when possible

See merge request gitlab-org/gitlab-ce!31915

Currently, the DB migrations guide says that "you must" use non-blocking
operations (such as CREATE INDEX CONCURRENTLY), always.

But this does not make sense in cases of empty tables and leads to
splitting the work to multiple non-atomic
(with disable_ddl_transaction!) DB migrations.

To follow KISS principle, to have fewer DB migrations steps,
to have them atomic when it's possible and simplify deployment
and troubleshooting, the following exceptions were added
to the doc:

- index creation,
- index dropping,
- defining an FK,
- adding a column with DEFAULT,

Run markdownlint before Nanoc checks

See merge request gitlab-org/gitlab-ce!32256

Make it simpler to run markdownlint by moving it before
we do those hacks to run Nanoc.

Promote Label to Group Label via API endpoint

Closes #57657

See merge request gitlab-org/gitlab-ce!25218

Update index of feature flags

See merge request gitlab-org/gitlab-ce!32217

Made it clear the pages are about feature flags,
and not documentation.

Update capitalization in /dev docs

See merge request gitlab-org/gitlab-ce!32189

Clean up capitalization in /development /gitlab-basics and
/install

Update capitalization in /integrations and /raketasks

See merge request gitlab-org/gitlab-ce!32241

Also updates redirect text in /project-services

Remove N+1 SQL query loading project feature in dashboard

Closes #66482

See merge request gitlab-org/gitlab-ce!32169

[#2838] add cache override explanation

See merge request gitlab-org/gitlab-ce!32024

Update `only` `chat` statement to correct singular form

See merge request gitlab-org/gitlab-ce!32116

Remove passing tests from quarantine

Closes gitlab-org/quality/nightly#127

See merge request gitlab-org/gitlab-ce!32237

Add missing blank line to omniauth doc

See merge request gitlab-org/gitlab-ce!32250

Resolve "Store deploy tokens encrypted"

Closes #63502

See merge request gitlab-org/gitlab-ce!30679

Reduce the complexity of our CI configuration

Closes #51367 and #65702

See merge request gitlab-org/gitlab-ce!31728

Add option to allow OAuth providers to bypass two factor

Closes #56059

See merge request gitlab-org/gitlab-ce!31996

allow_bypass_two_factor configration dose not work with saml provider

Docs: Remove mention of Kubernetes service templates

See merge request gitlab-org/gitlab-ce!32093

Update doc/api/events.md

See merge request gitlab-org/gitlab-ce!32071

Added migrations to make token column accepting null values and to add
encrypted token column.

CI Yaml configuration docs for using job rules

See merge request gitlab-org/gitlab-ce!32026

Fix Piwik not working

Closes #66627

See merge request gitlab-org/gitlab-ce!32234

Due to indentation, the changes in
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/31402 broke the
templating of Piwik script header.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/66627

Guard against deleted project feature entry

Closes #66482

See merge request gitlab-org/gitlab-ce!32187