When an admin creates a project in the namespace of a user, that user
automatically gains master access to that project.

It does more than solely GitLab Markdown, so rename to MarkupHelper.

- Ignore JS fixtures
- Ignore qa directory
- Rewrite concern specs to put concern name first

Turn ExpirePipelineCacheService into Worker so it can fetch all the
merge requests for which the pipeline runs or did run against.

- While deleting a user, some of the user's associated records are moved to the
  ghost user so they aren't deleted. The user is blocked before these records
  are moved, to prevent the user from creating new records while the migration
  is happening, and so preventing a data race.

- Previously, if the migration failed, the user would _remain_ blocked, which is
  not the expected behavior. On the other hand, we can't just stick the block +
  migration into a transaction, because we want the block to be committed before
  the migration starts (for the data race reason mentioned above).

- One solution (implemented in this commit) is to block the user in a parent
  transaction, migrate the associated records in a nested sub-transaction, and
  then unblock the user in the parent transaction if the sub-transaction fails.

Customers were surprised by the previous behavior, which destroyed branches
even though an open merge request existed for it.

Closes #29427

In the case of spammers, we really want a hard delete to avoid retaining spam.

Closes #31021

1. Extract out into several methods.
2. Add more comments describing the data and the shape of the data.

This table shows the percentage of users who registered in the last
twelve months, who last signed in during or later than each of those
twelve months, by month.

It is only enabled when the usage ping is enabled, and the page also
shows pretty-printed usage ping data.

The cohorts table is generated in Ruby from some basic SQL queries,
because performing the gap-filling and running sums needed in both MySQL
and Postgres is painful.

This new class uses a Redis Hash instead of a Sorted Set.
Signed-off-by: NRémy Coutable <remy@rymai.me>

Refactored specs and added a post deployment migration to remove the activity users table.

It uses a user activity table instead of a column in users.
Tested with mySQL and postgreSQL

Also poll for pipeline changes on:
 - Pipeline table on commit page
 - Pipeline table on merge request page
 - Pipeline table on new merge request page

Enable caching in the Etag::Middleware and when a pipeline changes
status, expire the cache for the project pipelines path.

1. Have `MigrateToGhostUser` be a service rather than a mixed-in module, to keep
   things explicit. Specs testing the behavior of this class are moved into a
   separate service spec file.

2. Add a `user.reported_abuse_reports` association to make the
   `migrate_abuse_reports` method more consistent with the other `migrate_`
   methods.

... when the user is destroyed.

1. Normally, for a given awardable and award emoji name, a user is only allowed
   to create a single award emoji.

2. This validation needs to be removed for ghost users, since:

   - User A and User B have created award emoji - with the same name and against
     the same awardable
   - User A is deleted. Their award emoji is moved to the ghost user
   - User B is deleted. Their award emoji needs to be moved to the ghost user.
     However, this breaks the uniqueness validation, since the ghost user is
     only allowed to have one award emoji of a given name for a given awardable

... when the user is destroyed.

To clarify, this regards abuse reports that the to-be-deleted user has _reported_.

... when the user is destroyed.

1. When the user is deleted.

2. Refactor out code relating to "migrating records to the ghost user" into a
   `MigrateToGhostUser` concern, which is tested using a shared example.