Here I make and propose some final changes to our current metrics for the release of Qdrant 1.16.0.

Specifically this does:

1. re-adds collections_vector_total metric (for backwards compatibility)
2. namespaces new replica metrics with collection_ (to best follow my interpretation of recommendations):
   • active_replicas_{min,max} -> collection_active_replicas_{min,max}
   • dead_replicas -> collection_dead_replicas
3. count collection_running_optimizations per collection, as I think that's much more interesting in practice

We keep the new qdrant_ prefix disabled for all metrics to not break existing deployments. Users have control over the prefix if they ever want to enable it for their deployment.

Please see this PR as a request for comment. If we're happy with this final result, we can merge.

Here is a dump of all metrics: https://gist.github.com/timvisee/6a3e7968bcfc63b3cc1471788ca9ccbc

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