Azure Monitor: Azure Resource Graph - Filter By Management Group

**Why is this needed**: Sometimes you want to run Azure Resource Graph Queries against all subscriptions in a management group. The API supports filtering by Management Group but the datasource doesn't. You can only filter by subscriptions there. Manually selecting every subscription in a certain Management Group is not an option because new subscription may be created over time and these new subscriptions would not be automatically included in the query. See API docs: https://learn.microsoft.com/en-us/rest/api/azureresourcegraph/resourcegraph/resources/resources?view=rest-azureresourcegraph-resourcegraph-2024-04-01&tabs=HTTP#request-body **What would you like to be added**: Add an option to filter by management group and make the subscription filter optional. In a more general sense: Just make the filter options exactly as in the API. The subscription filter should not be required as it is also not required in the API. This issue goes in a similiar direction: https://github.com/grafana/grafana/issues/82793 **Who is this feature for?** Everyone who uses Azure Resource Graph in the Azure Monitor datasource.