Migrate simple user_delete_request endpoints from Drupal

Related to #35 (closed)

This MR:

• Adds a user_delete_request table, DTO, and model
• Adds filtered list endpoint
• Adds single request fetch endpoint
• Adds update endpoint
• Adds delete endpoint
• Adds testing for all these endpoints

This MR does not include the main POST endpoint that receives the initial deletion request for a user.