Move service desk to core

This is a follow up of #214839 (closed) which moves service desk from Premium to Core 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)