Identity for AzureSearch

[Paul-B98]

Describe the current behavior

Currently, it is only possible to assign a SystemAssigned identity to an Azure search template. In addition, there is no documented behaviour that shows how to access the principal ID of the identity.

Describe the improvement

1. To make a role assignment, it would be helpful to access the principal id of the SystemAssigned identity in a similar way to the SearchServiceOperatorSpec.
2. Another option is to enable a user identity for Azure Search. This should be possible if you check the documentation for the Azure search template.

Additional context

• Bicep Doc

[theunrepentantgeek]

It appears UserAssigned requires upgrading to the 2023-11-01 version the Microsoft.Search API; that should be straightforward.

I'm not sure about how to expose the system assigned identity, but I think @matthchr will know.