Draft: Add `report_type` for Project API

What does this MR do and why?

This MR exposes report_type field for Project API. The field is under project's approval rules.

The reason to expose it is terraform needs the field to be returned. After creating a project with report_type, Terraform will fetch the field of the Project to confirm, but currently GitLab API doesn't return report_type field.

Related to Allow Automated Creation of the Coverage-Check ... (terraform-provider-gitlab#1402).

Screenshots or screen recordings

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

$ curl \
--header "PRIVATE-TOKEN: $TOKEN" \
"http://YOUR_DOMAIN/api/v4/projects/:id/approval_rules"

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.