This will be used later for search filtering.

Add spec to test different combinations.

Detect if pipeline runs for a GitHub pull request

When using a mirror for CI/CD only we register a pull_request
webhook. When a pull_request webhook is received, if the
source branch SHA matches the actual head of the branch in the
repository we create immediately a new pipeline for the
external pull request. Otherwise we store the
pull request info for when the push webhook is received.

When using "only/except: external_pull_requests" we can detect
if the pipeline has a open pull request on GitHub and create or
not the job based on that.

This change limits the number of emails
for new access requests notifications to
10 most recently active owners/maintainers

The flag defaulted to true, so there's no change unless users turned it
off. Given there's a lack of issues regarding object pools, this should
be OK.

This change lays the foundation for customizable cycle analytics stages.
The main reason for the change is to extract the event definitions to
separate objects (start_event, end_event) so that it could be easily
customized later on.

- Adds UI to configure in group and project settings
- Removes notification configuration for users when
disabled at group or project level

**Prevention of running 2 simultaneous updates**

Instead of using `RemoteMirror#update_status` and raise an error if
it's already running to prevent the same mirror being updated at the
same time we now use `Gitlab::ExclusiveLease` for that.

When we fail to obtain a lease in 3 tries, 30 seconds apart, we bail
and reschedule. We'll reschedule faster for the protected branches.

If the mirror already ran since it was scheduled, the job will be
skipped.

**Error handling: Remote side**

When an update fails because of a `Gitlab::Git::CommandError`, we
won't track this error in sentry, this could be on the remote side:
for example when branches have diverged.

In this case, we'll try 3 times scheduled 1 or 5 minutes apart.

In between, the mirror is marked as "to_retry", the error would be
visible to the user when they visit the settings page.

After 3 tries we'll mark the mirror as failed and notify the user.

We won't track this error in sentry, as it's not likely we can help
it.

The next event that would trigger a new refresh.

**Error handling: our side**

If an unexpected error occurs, we mark the mirror as failed, but we'd
still retry the job based on the regular sidekiq retries with
backoff. Same as we used to

The error would be reported in sentry, since its likely we need to do
something about it.

This commit reduces I/O load and memory utilization during PostReceive
for the common case when no project hooks or services are set up.

We saw a Gitaly N+1 issue in `CommitDelta` when many tags or branches
are pushed. We can reduce this overhead in the common case because we
observe that most new projects do not have any Web hooks or services,
especially when they are first created. Previously, `BaseHooksService`
unconditionally iterated through the last 20 commits of each ref to
build the `push_data` structure. The `push_data` structured was used in
numerous places:

1. Building the push payload in `EventCreateService`
2. Creating a CI pipeline
3. Executing project Web or system hooks
4. Executing project services
5. As the return value of `BaseHooksService#execute`
6. `BranchHooksService#invalidated_file_types`

We only need to generate the full `push_data` for items 3, 4, and 6.

Item 1: `EventCreateService` only needs the last commit and doesn't
actually need the commit deltas.

Item 2: In addition, `Ci::CreatePipelineService` only needed a subset of
the parameters.

Item 5: The return value of `BaseHooksService#execute` also wasn't being
used anywhere.

Item 6: This is only used when pushing to the default branch, so if
many tags are pushed we can save significant I/O here.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/65878

Fic

As decided in https://gitlab.com/gitlab-org/gitlab-ce/issues/53593

Kubernetes deployments on new clusters will now have
a separate namespace per project environment, instead
of sharing a single namespace for the project.

Behaviour of existing clusters is unchanged.

All new functionality is controlled by the
:kubernetes_namespace_per_environment feature flag,
which is safe to enable/disable at any time.

Add spec for cases where URI.join does not work as expected

All cluster resources are now created on demand when
a deployment job starts.

* Reword Project#latest_successful_build_for to
Project#latest_successful_build_for_ref
* Reword Ci::Pipeline#latest_successful_for to
Ci::Pipeline#latest_successful_build_for_ref

These are not required because MySQL is not
supported anymore

- Fix `O(n)` complexity of `append_or_update_attribute`,
  we append objects to an array and re-save project
- Remove the usage of `keys.include?` as it performs `O(n)`
  search, instead use `.has_key?`
- Remove the usage of `.keys.first` as it performs a copy
  of all keys, instead use `.first.first`

Adds specs for testing the new behavior of specifying a pipeline when
POSTing a status.

This pagination is not used anywhere so there is no reason
to keep it. It seems the usage of offset_id was probably
removed in 90c60138

Now we have terminals for instance and group clusters we can remove the
FF now. Deploying to group clusters has been working without complaints
too.

Project-level clusters that made use of this legacy
behaviour have been migrated to unmanaged clusters,
so we are now free to remove this fallback.

We are deprecating this service in favor of instance wide clusters.
Therefore we removed some code that is not anymore needed for a
readonly cluster and also we added some flags to allow for this
deprecation. These flags are to be removed in the next release when
we finally completelly remove KubernetesService.