Add RemoteWrite Support for Centralized Metrics Aggregation

[martincarrere]

Is your feature request related to a problem?
In addition to using the Ceph Stack, we aggregate all our metrics under a Thanos cluster. To enhance observability and streamline monitoring, I would like to centralize all metrics in the same HA & Long terme retention store.

Describe the solution you'd like
Would it be possible to add support for the remoteWrite feature as an argument within this template _https://github.com/ceph/ceph-ansible/blob/main/roles/ceph-prometheus/templates/prometheus.yml.j2_.This would enable direct integration with our Thanos setup.

Describe alternatives you've considered
An alternative approach would be to deploy an additional metrics collector to pull data from Prometheus and push it to our Thanos tenant. However, integrating remoteWrite directly would simplify the architecture and reduce operational overhead.

Additional Context
This enhancement would provide a more seamless experience for organization leveraging Thanos for long-term storage and centralized monitoring. While Thanos is our use case, this feature would also benefit any setup leveraging a long-term storage backend (e.g., Mimir, Cortex, VictoriaMetrics, ...).