feat: Migrate main user_delete_request endpoint from Drupal

Related to: #35 (closed)

Related to: #55 (closed)

Here is a brief overview of the changes within this rather large MR:

• Adds AccountRequests DDL and DTO
• Updates the openAPI spec
• Adds missing class-level comments
• Adds additional logging
• Adds support for api-common 0.7.4-SNAPSHOT
• Adds authentication to all user_delete_request endpoints
• Restructures the Resource classes to better separate concerns, grouped by URL
• Major refactor of services:
  • Repurpose MetaDataService from a wrapper for RestClients, to a service that handles all user metadata.
  • Remove all metadata related processing from the ProfileService and restrict it to processing only base profile data
• Adds MetadataHelper and UserDeleteHelper helper classes
• Adds authentication testing for existing user delete endpoints
• Adds POST user delete request endpoint + testing