Amtool throwing an error as 'scheme required for webhook url' in RHOCP 4

Issue

• Getting an error as scheme required for webhook url in amtool:

  $ oc exec alertmanager-user-workload-0 -- amtool config routes test severity=critical --alertmanager.url http://localhost:9093
  amtool: error: scheme required for webhook url
  
  command terminated with exit code 1