Add API route for total network objects

[maxalbert]

flowmachine.features.network.total_network_objects.TotalNetworkObjects` should have an exposed API route.

The parameters to be exposed are similar to other exposed routes. I suggest to expose start (as start_date), stop (as end_date) and level (as aggregation_unit) to begin with.

• Add TotalNetworkObjectsExposed class
• Add marshmallow schema
• Add schema to FlowmachineQuerySchema
• Add flowclient function
• Add tests to integration tests (in integration_tests/tests/test_queries.py)
• Add query endpoint to Flowauth demo data
• Update approval test data for integration tests