Move service desk to core
This is a follow up of #214839 (closed) which moves service desk from Premium to Starter with a simple change to license file.
Moving service desk to core can be broken down into some tasks:
Backend
- Move support bot related to code to core !34883 (merged)
- Remove licence checks: !35444 (merged)
- Move backend models/api code: !35557 (merged)
- Move backend controllers/services code !35666 (merged)
- Move backend mailers/workers code !36132 (merged)
- Move usage data to core !37080 (merged)
Frontend
- Move frontend files !36613 (merged)
- Update documentation !37116 (merged)
Follow up improvements
- Add translations for frontend files including emails !37705 (merged)