Remove design git repos when deleting a project

What does this MR do and why?

Related issue: #361356 (closed)

Remove design git repos when deleting a project

Avoid orphaning design git repos when projects are deleted

Screenshots or screen recordings

How to set up and validate locally

1. Setup a project with a design repo, ensure the git repo exists

p = Project.first
p.design_repository
p.design_management_repository.create_if_not_exists
raw_repo = p.design_repository.raw_repository
raw_repo.exists? # should be true

2. Destroy the project: Projects::DestroyService.new(p, User.first).execute # assuming User.first has remove_project permission
3. Check if the repo still exists: raw_repo.exists? # should be false

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.