Firewall collection updates

Reviewed existing Firewall endpoints and schemas

Added:
- GET /networking/firewalls/{firewallId}/devices
- POST /networking/firewalls/{firewallId}/devices
- GET /networking/firewalls/{firewallId}/devices/{deviceId}
- DELETE /networking/firewalls/{firewallId}/devices/{deviceId}
- GET /networking/firewalls/{firewallId}/rules
- POST /networking/firewalls/{firewallId}/rules

Author: nmelehan