[373705] Configurable GitHub import optional stages list API

What does this MR do and why?

Implementation for Configurable list of things 'to be imported' that can be adjusted by the user (API)

Screenshots or screen recordings

JSON API

Logs proves that optional stages were executed by submitted config via JSON API:

How to set up and validate locally

Use postman or different tool to make an API request to: POST http://localhost:3000/api/v4/import/github

An example of payload:

{
  "personal_access_token":"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",
  "repo_id":481255171,
  "target_namespace":"root",
  "new_name":"test-flags",
  "optional_stages": {
    "single_endpoint_issue_events_import":true,
    "single_endpoint_notes_import":false,
    "attachments_import":false
  }
}

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