[tf] Add self monitoring relations

[sed-i]

Via @simskij:

Loki is not ingesting it's own logs. what's missing is:

• a grafana agent
• relation over loki:logging-consumer to ga
• relation over loki:logging-provider to ga

Loki is not sending any metrics to mimir. what's missing is:

• a grafana agent
• relation over loki:self-metrics-endpoint to ga, and
• relation over mimir:receive-remote-write to ga

Tempo is not sending any metrics to mimir. what's missing is:

• a grafana agent
• relation over tempo:self-metrics-endpoint to ga, and
• relation over mimir:receive-remote-write to ga
• :logging relation

:tracing relation is missing for all charms that support it:

        juju relate tempo:tracing loki
        juju relate tempo:tracing mimir
        juju relate tempo:tracing grafana:tracing
        juju relate tempo:tracing loki:tracing
        juju relate tempo:tracing loki-backend:tracing
        juju relate tempo:tracing loki-read:tracing
        juju relate tempo:tracing loki-write:tracing
        juju relate tempo:tracing mimir-alertmanager:tracing
        juju relate tempo:tracing mimir-compactor:tracing
        juju relate tempo:tracing mimir-distributor:tracing
        juju relate tempo:tracing mimir-flusher:tracing
        juju relate tempo:tracing mimir-ingester:tracing
        juju relate tempo:tracing mimir-overrides-exporter:tracing
        juju relate tempo:tracing mimir-querier:tracing
        juju relate tempo:tracing mimir-query-frontend:tracing
        juju relate tempo:tracing mimir-query-scheduler:tracing
        juju relate tempo:tracing mimir-ruler:tracing
        juju relate tempo:tracing mimir-store-gateway:tracing
        juju relate tempo:tracing self-signed-certificates:tracing
        juju relate tempo:tracing traefik:tracing