Expose rocksDB metrics

**FEATURE REQUEST**

1. Please describe the feature you are requesting.

Expose rocks db metrics (statistics) in the `/metrics` endpoint. The motivation is to ensure the rocks db configuration is optimal.

2. Indicate the importance of this issue to you (blocker, must-have, should-have, nice-to-have).
Are you currently using any workarounds to address this issue?

This feature should help make it easier to tune the different rocks db configurations.

3. Provide any additional detail on your proposed use case for this feature.

It looks like these statistics are exposed through the `DBOptions` object. I plan to help implement these metrics.

It might be worth putting these metrics behind a feature flag.

Start by locating the `/metrics` endpoint and inspecting the `DBOptions` object for the available RocksDB statistics. Determine how those statistics should be exposed and whether a feature flag is needed; done means the selected metrics are available through `/metrics`.

Written by the indexing model from the issue text.