This adds support for using the database load balancer with multiple
databases. Load balancing is applied to two classes:

- ActiveRecord::Base
- Ci::CiDatabaseRecord

Each class has its own load balancer, configuration, service discovery,
etc. Load balancing for the CI class is only enabled when a CI
configuration exists, as it can reuse the main load balancer when
there's no dedicated CI database.

Sticking technically supports multiple databases, but in practise we
apply the same sticking rules to all databases. This is due to how
LoadBalancing::Session is used: there is only one instance per
request/Sidekiq job, and it's not aware of what database connections did
what. This means that a write to database A will result in GitLab
sticking to the primaries of _all_ databases. The choice for this is
simple: it requires fewer code changes, and allows us to introduce
multiple database support in smaller increments.

One change we made to sticking is to turn the Sticking module into a
class, and attach an instance to every base module that has its own load
balancer. This makes it easier to apply sticking on a per-database level
in the future, without having to type
`Gitlab::Database::LoadBalancing::Sticking...` every time.

Sticking also supports reading and writing of data using the old Redis
key names. This ensures sticking continues to work during a deployment,
as during this window we'll run two different versions in production.
Once the code has been deployed to GitLab.com and has been confirmed to
work, we'll remove support for reading/writing the old keys.

Sidekiq also supports load balancing multiple databases. If a load
balancer/database doesn't have any WAL data in the Sidekiq job, we treat
the database as being in sync. This way we can support Sidekiq jobs
using both the old and new load balancing data.

See https://gitlab.com/gitlab-org/gitlab/-/issues/331776 for more
details.

Changelog: added

Fix misplaced secure product metrics definitions

See merge request gitlab-org/gitlab!71799

Fix incorrect cycle time metric definition

See merge request gitlab-org/gitlab!71733

Upgrade to test-prof 1.0.7

See merge request gitlab-org/gitlab!71893

Remove feature flag disable_joins_upstream_downstream_projects

See merge request gitlab-org/gitlab!71968

Gracefully track errors raised by sending CI minutes notifications

See merge request gitlab-org/gitlab!71815

Use pessimistic locking when accessing Terraform state

See merge request gitlab-org/gitlab!71873

[VSA] Update cycle time UI text

See merge request gitlab-org/gitlab!71823

Refactor browser per widget to extension

See merge request gitlab-org/gitlab!71330

Use prefix js- to class names

See merge request gitlab-org/gitlab!71546

Split Snowplow docs' headers to make important content more accessible

See merge request gitlab-org/gitlab!71608

Fixes tooltip label for load performance in widget extension

See merge request gitlab-org/gitlab!71942

Merge branch '299509-improve-the-location-of-where-the-runner-registration-information-lives' into 'master'

Remove redundant help text from runners

See merge request gitlab-org/gitlab!71915

Remove sync_namespace_name_with_cdot flag

See merge request gitlab-org/gitlab!71763

Doc Consistency: ci/variables

See merge request gitlab-org/gitlab!69785

Doc Consistency: ci

See merge request gitlab-org/gitlab!69787

Doc Consistency: ci/pipelines

See merge request gitlab-org/gitlab!69779

Remove redundant includes in end to end tests

See merge request gitlab-org/gitlab!69117

Migrate milestone filter Bootstrap tabs to GlTabs

See merge request gitlab-org/gitlab!71710

Use account id as part of the namespace to init Zuora iframe

See merge request gitlab-org/gitlab!71735

Rename utils/worker to tree_worker_utils

See merge request gitlab-org/gitlab!63561

Vue Shared - Dropdown Keyboard Navigation

See merge request gitlab-org/gitlab!71206

Add local time to user popover

See merge request gitlab-org/gitlab!70806

Fix mark snippet as spam button

See merge request gitlab-org/gitlab!71070

Don't try to run database helpers as specs

See merge request gitlab-org/gitlab!71929

Refactor: moving and renaming timeSummaryForPathNavigation

See merge request gitlab-org/gitlab!71895

Disable `Vulnerabilities::Finding` joins in `Ci::Pipeline`

See merge request gitlab-org/gitlab!70216

Return the correct project in job/allowed_agents API response

See merge request gitlab-org/gitlab!71876

Admin page to list user's credit card matches

See merge request gitlab-org/gitlab!71533