Add Filter for NewListForScopePager on RoleManagementPolicyAssignmentsClient

### Feature Request

I am creating a Terraform resource to manage RoleManagementPolicies through terraform. I am looking to use the RoleManagementPoliciesClient to list role management policies for a given `scope` and `roleDefinitionId` to then load the existing RoleManagementPolicy. However, the `NewListForScopePager` does not allow specifying a `Filter`.

There is `Filter` support on other List methods and you are able to filter directly on the REST method (see: https://docs.microsoft.com/en-us/rest/api/authorization/privileged-role-policy-rest-sample)

`https://management.azure.com/providers/Microsoft.Subscription/subscriptions/{{subscription-id}}/providers/Microsoft.Authorization/roleManagementPolicies?api-version=2020-10-01-preview&filter=roleDefinitionId eq '/subscriptions/********-****-****-****-************/providers/Microsoft.Authorization/roleDefinitions/********-****-****-****-************'`

This will return you the roleManagementPolicy for the request subscription and role.

Could support for `Filter` be added to this method?

EDIT
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I had originally quoted the above API call which is incorrect, the correct call is to retreive a RoleManagementPolicyAssignment for a scope/roleDefinitionId, this can be acheived with the following API call

`https://management.azure.com/subscriptions/{{subscription-id}}/providers/Microsoft.Authorization/roleManagementPolicyAssignments?api-version=2020-10-01&$filter=roleDefinitionId eq '/subscriptions/********-****-****-****-************/providers/Microsoft.Authorization/roleDefinitions/********-****-****-****-************'`

So this applies to the `RoleManagementPolicyAssignmentsClient` and would request the addition of the `Filter` property.

Have tested in Postman with the above query and it does return the result for the scope/roleDefinitionId combination.

Start by locating the RoleManagementPolicyAssignmentsClient.NewListForScopePager definition and its corresponding REST API specification. Check how the list operation represents the $filter query parameter, then verify that the generated request supports filtering by roleDefinitionId as shown in the issue's REST URL.

Written by the indexing model from the issue text.