IssuableBaseService has been updated so that labels are not
created when push options to remove them are received.

MergeRequests::PushOptionsHandlerService has been updated to allow
adding and removing labels to a merge request using git push options.

To create a new merge request and add 2 labels to it:

      git push -u origin -o merge_request.create \
        -o merge_request.label="My label 1" \
        -o merge_request.label="My label 2"

To update an existing merge request and remove a label while
adding a different label:

      git push -u origin -o merge_request.label="My added label" \
        -o merge_request.unlabel="My removed label"

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

Suggests to use a JSON structured log instead

Related to https://gitlab.com/gitlab-org/gitlab-ce/issues/54102

- labels have to be in the same project/group
as an issuable

Signed-off-by: Rémy Coutable <remy@rymai.me>

This commit adds the module `FromUnion`, which provides the class method
`from_union`. This simplifies the process of selecting data from the
result of a UNION, and reduces the likelihood of making mistakes. As a
result, instead of this:

    union = Gitlab::SQL::Union.new([foo, bar])

    Foo.from("(#{union.to_sql}) #{Foo.table_name}")

We can now write this instead:

    Foo.from_union([foo, bar])

This commit also includes some changes to make this new setup work
properly. For example, a bug in Rails 4
(https://github.com/rails/rails/issues/24193) would break the use of
`from("sub-query-here").includes(:relation)` in certain cases. There was
also a CI query which appeared to repeat a lot of conditions from an
outer query on an inner query, which isn't necessary.

Finally, we include a RuboCop cop to ensure developers use this new
module, instead of using Gitlab::SQL::Union directly.

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/51307

This whitelists all existing offenses for the various CodeReuse cops, of
which most are triggered by the CodeReuse/ActiveRecord cop.

This whitelists all existing places where we use "destroy_all".

For directories application_settings --> labels.

Partially addresses #47424.

Allow Labels::FindOrCreateService to find ancestor group labels
Add authentication check on API endpoint
Update flayignore

Adds a rubocop rule (with autocorrect) to ensure line break after guard clauses.

This reverts commit cb10b725c8929b8b4460f89c9d96c773af39ba6b.

Fixes #24021

Fix label creation non members

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/23416

See merge request !2006

Do not pass project.owner because it may return a group and Labels::FindOrCreateService
throws an error in this case.
Fixes #23694.

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>