correct the prometheus feature configuration according to https://gitlab.com/git…

See merge request !8703

Add Prometheus docs

See merge request !8699

This MR enables rendering of PlantUML diagrams in Asciidoc documents. To add a
PlantUML diagram all we need is to include a plantuml block like:

```
[plantuml, id="myDiagram", width="100px", height="100px"]
--
bob -> alice : ping
alice -> bob : pong
--
```

The plantuml block is substituted by an HTML img element with *src* pointing to
an external PlantUML server.

This MR also add a PlantUML integration section to the Administrator -> Settings
page to configure the PlantUML rendering service and to enable/disable it.

Closes: #17603

Log LDAP blocking/unblocking events to application log

See merge request !8042

Fix dead link in Reply by email documentation

Closes #26247

See merge request !8474

Clarify git housekeeping

See merge request !8373

This changed in
https://gitlab.com/gitlab-org/gitlab-ce/commit/6bcc52a53678ca68001189c801497862d3f6e758

The current docs are not clear in stating that we also run a `git repack` and
that we respect the admin application setting values.

This adds counters for build artifacts and LFS objects, and moves
the preexisting repository_size and commit_count from the projects
table into a new project_statistics table.

The counters are displayed in the administration area for projects
and groups, and also available through the API for admins (on */all)
and normal users (on */owned)

The statistics are updated through ProjectCacheWorker, which can now
do more granular updates with the new :statistics argument.

Added support for Authentiq OAuth provider

See merge request !8038