Add option to limit legacy uploads size

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Summary

For https://gitlab.com/gitlab-org/gitlab/-/issues/31178 we want to limit the size of design uploads. These go through Workhorse so we need to add a setting there.

Improvements

• On Rails side update autorize_upload endpoint to return also maximum_size (related to discussion #324874 (comment 1129778943)):
  • this should be generous enough value it works for any uploads which use this generic endpoint
  • ideally this should be rolled-out carefully (behind a feature flag)
  • this maximum_size value should be configurable (so admins can update this instead of waiting for patch release in case we would set this limit too low)
• Enforce this limit when handling legacy uploads. Uploads that are too large should be rejected with a 413 Request Entity Too Large error.
  • assuming that we return maximum_size value in autorize_upload response, this should work automatically out-of-the box (same as for direct uploads)

Risks

Involved components

• HandleFileUploads in internal/upload/uploads.go
  • There's an existing check which returns filestore.ErrEntityTooLarge, we can reuse the same error in our check.
• Configuration file handling is in internal/config/config.go

Optional: Intended side effects

Optional: Missing test coverage