Adds migration to rename project_mirror_data table to project_import_state and…

What does this MR do?

Moves some import related attributes out of the projects table

Why was this MR needed?

Better explained in: https://gitlab.com/gitlab-com/infrastructure/issues/3910

TODO

• Replace occurrences of the old fields with the new fields
  • import_status
  • mirror_data
  • import_jid
  • mirror_last_update_at
  • mirror_last_successful_update_at
  • import_error
  • migrate the state machine to ProjectImportState
  • Clear all the TODO statements

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• Tests added for this feature/bug
• Review
  • Has been reviewed by Backend
  • Has been reviewed by Database
• EE specific content should be in the top level /ee folder
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together
• End-to-end tests pass (package-qa manual pipeline job)

What are the relevant issue numbers?

https://gitlab.com/gitlab-org/gitlab-ce/issues/44542