text: Title: Further tweak the alerting functional test to use limited privileges. 
  Body: As a follow up to https://github.com/elastic/kibana/pull/88727, we could further tweak this test to use limited set of privileges ( roles) assigned to the `test_user` instead of giving it `all` . Here is a Meta issue linked for this effort: https://github.com/elastic/kibana/issues/60815
  
  
  It would also be prudent to convert other such tests which fall under Alerting umbrella
  
  cc @LeeDr @elastic/kibana-alerting-services 