* Cleaned issues and issues_statistics docs
* Renamed param with_labels_data to with_labels_details
* Added spec for N+1 check when retrieving labels from issue
* Refactoed CheckAssigneesCount validation class
Remove label_name and milestone_title params support
Add mutually_exclusive validation for author_id and author_username
Add mutually_exclusive validation for assignee_id and assignee_username
Add validation to allow single value for asignee_username on CE
Add separate issue_stats_params helper for statistics params and
reuse in issues_params.
A malicious attacker could craft a request to read arbitrary files on
the system. This change adds a Grape validation to ensure that the
tempfile parameter delivered by the Rack multipart uploader is a
Tempfile type to prevent users from being able to specify arbitrary
filenames.
Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/53072
