[FEATURE] Support to specify backend roles for detectors

[amitgalitz]

Is your feature request related to a problem?
There should be a way to associate specific backend roles for detectors during create and update process.
Currently there is no way for an admin to change the backend roles for a specific detector or create a detector with a particular set of backend roles.

What solution would you like?
We should implement a similar solution to what is done in alerting here: opensearch-project/alerting#635. A user should be able to specify backend roles for the detectors with an additional field to API call.

During AD create:

User adds backend role field to the API:

• Admin users: Use all the specified backend roles to associate to the detector
• Normal user: Use all the specified backend roles that the user already has in there backend role list to associate to the detector.

User doesn't add backend role field:

• Copy user’s backend roles and associate them to the monitor

During AD update:

User adds backend role field to the API:

• Admin user: Remove all the backend roles associated to the detector and then use all the specified backend roles to associate to the detector
• Normal user: Remove backend roles associated to the detector that the user has access to, but didn’t specify. Then add all the other specified backend roles (that the user already has in their list of backend roles) to the detector

User doesn't add backend role field:

• Don’t update the backend roles on the monitor