[Authorization] Role Assignments - List: The doc for `$filter` is incomplete

[jiasli]

The doc for $filter is incomplete for listing role assignments APIs, like Role Assignments - List and Role Assignments - List For Scope.

azure-rest-api-specs/specification/authorization/resource-manager/Microsoft.Authorization/stable/2015-07-01/authorization-RoleAssignmentsCalls.json

Lines 83 to 87 in e83bb33

	"name": "$filter",
	"in": "query",
	"required": false,
	"type": "string",
	"description": "The filter to apply on the operation. Use $filter=atScope() to return all role assignments at or above the scope. Use $filter=principalId eq {id} to return all role assignments at, above or below the scope for the specified principal."

According to https://docs.microsoft.com/en-us/azure/role-based-access-control/role-assignments-list-rest#list-role-assignments, assignedTo is also supported.

Thanks for the feedback! We are routing this to the appropriate team for follow-up. cc @darshanhs90, @AshishGargMicrosoft.