Follow-up: Prohibit GitLab for Jira Cloud app API being enabled, or disabled, through API

The following discussion from !159331 (merged) should be addressed:

• @bmarjanovic started a discussion: (+1 comment)

  though/suggestion: this will prevent editing from UI, and what about the api 🤔

  If I recall correctly, we used to have something in place for preventing editing, but not sure if that has changed.

  Anyhow, I think we should also update lib/api/integrations.rb to include something like:

  if !integration.new_record? && integration.editable?
    render_api_error!("You cannot edit the #{integration.title} integration from the API", 403)
  end