[FEATURE] Validate trigger names and ensure there are no duplicate names in the same monitor

[lezzago]

Is your feature request related to a problem? Trigger names are not validated to see if there are other triggers in the same monitor with the same name

What solution would you like? Prevent monitors from being created where the monitor have triggers with the same name

[lezzago]

This can be optional on the backend and keeping this issue open here to decide if we want backend validation.

Related front end issue: https://github.com/opensearch-project/alerting-dashboards-plugin/issues/671