[feature] Add InfluxDB 2 and Elasticsearch support to RADIUS monitoring

Depends on https://github.com/openwisp/openwisp-monitoring/issues/848.

Is your feature request related to a problem? Please describe.

openwisp_radius.integrations.monitoring supports only InfluxDB 1. Its six chart configurations use InfluxQL, and rebuild_radius_accounting_metrics issues a raw InfluxQL deletion query.

As a result, enabling the RADIUS monitoring integration with InfluxDB 2 or Elasticsearch prevents RADIUS registration, traffic, and unique-session charts from working.

Describe the solution you'd like

Add InfluxDB 2 and Elasticsearch query definitions for all RADIUS monitoring charts while preserving their current behavior:

• User registrations, grouped by registration method.
• Total registered users, using the latest cumulative snapshot per time bucket.
• Device-specific and general RADIUS traffic, with upload and download values in GB.
• Device-specific and general unique RADIUS sessions, grouped by registration method.

Use the Monitoring time-series client API for rebuilding accounting metrics so the management command works with every supported backend.

Update the monitoring integration test configuration and CI to run the tagged RADIUS monitoring suite against InfluxDB 1, InfluxDB 2, and Elasticsearch.

Describe alternatives you've considered

Keeping the integration InfluxDB 1-only leaves RADIUS incompatible with supported Monitoring backends.

Adding backend-specific client calls throughout RADIUS would duplicate storage-layer behavior that belongs in OpenWISP Monitoring.

Additional context

InfluxDB 2 support was added to OpenWISP Monitoring in https://github.com/openwisp/openwisp-monitoring/pull/801.

Elasticsearch support was added to OpenWISP Monitoring in https://github.com/openwisp/openwisp-monitoring/pull/829.