WIP: Resolve "Scale deployments directly from the environment page"

What does this MR do?

Adds environment scaling capabilities to the backend.

Are there points in the code the reviewer needs to double check?

The check for scaling availability.

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
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together
• End-to-end tests pass (package-and-qa manual pipeline job)

What are the relevant issue numbers?

Related #38543 (moved)