Feature Add multi-environment/customer support for device filtering

[Dongalis]

The Application Study Tool currently treats all BIG-IP devices as a single group, with no way to filter or separate them by environment. This makes it difficult for organizations managing devices across multiple environments (production, staging, lab, etc.) to focus on the devices relevant to their use case.

Adding an environment label to devices would allow:

• Grafana dashboard filtering via a dropdown to select a specific environment or "All"
• Scoped device_name dropdown so selecting a device in Environment A doesn't show devices from Environment B

This would be configured in ast_defaults.yaml or per-BigIP in bigip_receivers.yaml:

# ast_defaults.yaml
environment: production

# bigip_receivers.yaml
receivers:
  bigip/1:
    host: 10.0.0.1
    environment: staging
  bigip/2:
    host: 10.0.0.2
    # inherits default: production