Concurrent calls to UserMergeToRef RPC updating a single ref
can lead to an opaque fail that is being rescued at Gitaly.

So this commit adds an exclusive lease to the mergeability
check process with the key as the current MR ID.

Resolve "Add system notes for when a zoom call was added/removed from an issue"

Closes #63547

See merge request gitlab-org/gitlab-ce!30857

Add a zoom link added / removed system note when a zoom link is being
added / removed to the issue description.

Filter params in MR build service

Closes #2879

See merge request gitlab/gitlabhq!3237

Support title and desc on merge w/ push option

See merge request gitlab-org/gitlab-ce!31068

MergeRequests::PushOptionsHandlerService has been updated to allow
creating and updating merge requests with the `title` and
`description` set using git push options.

To create a new merge request and set its title and description:

      git push -u origin -o merge_request.create \
        -o merge_request.title="My title" \
        -o merge_request.description="My description"

To update an existing merge request and set its title and
description:

      git push -u origin -o merge_request.title="My title" \
        -o merge_request.description="My description"

Issue https://gitlab.com/gitlab-org/gitlab-ce/issues/64320

Although `flat_map` is equivalent to `map` + `flatten(1)`
(note the level 1) we can apply this same refactoring to all cases.

Reusing the existing `IssuableBaseService#filter_params` which uses
the policies to determine what params a user can set, and which values
it can be set to.

This also removed the need for the seperate call to
`IssuableBaseService#ensure_milestone_available`.

The `Issues::BuildService` does not suffer from this because it limits
the params that are assignable to the `title`, `description` and
`milestone_id`.

MergeRequests::PushOptionsHandlerService has been updated to allow
creating and updating merge requests with the
`remove_source_branch` set using git push options.

To create a new merge request and set it to remove the source branch
when it is merged:

  git push -u origin -o merge_request.create \
    -o merge_request.remove_source_branch

To update an existing merge request and set it to remove the source
branch when it is merged:

  git push -u origin -o merge_request.remove_source_branch

Issue https://gitlab.com/gitlab-org/gitlab-ce/issues/64320