export StorageMetricsStore as prometheus metrics

[wolfchimneyrock]

Feature or Problem Description

we want to provide usage metrics to our tenants of schema registry - we are planning on using groups as the tenancy unit.

right now we are having to scrape the rest api at intervals to publish metrics about # of artifacts, # of artifact versions, size of artifacts per group. this seems pretty wasteful and will be scale linearly when we have a large number of groups onboard.

In io.apicurio.registry.storage.metrics.StorageMetricsStore these figures are being collected and used for quota enforcement. Can these also be exported into the prometheus metrics?

Proposed Solution

Additional Context

[carlesarnal]

We have recently started looking not only into this but also to log aggregation. You can expect to have news about this in the next major version of Apicurio Registry.