Document new Prometheus metrics

**PR:**
https://github.com/influxdata/influxdb/commit/dece95d

https://github.com/influxdata/influxdb/pull/22904

Document the new tsm compaction metrics via prometheus as part of the InfluxDB v2.2 release

##### Relevant URLs
(https://docs.influxdata.com/influxdb/v2.1/reference/prometheus-metrics/#resulting-line-protoco)

Metrics are here:
https://github.com/influxdata/influxdb/commit/dece95d

From the release notes:

- Add Prometheus metrics for TSM compactions, including:
- `storage_compaction`
- `storage_compactions_active`
- `storage_compactions_duration_seconds_bucket`
- `storage_compactions_duration_seconds_count`
- `storage_compactions_duration_seconds_sum`
- `storage_compactions_queued`
- `storage_compactions_total`

Start with the existing Prometheus metrics documentation at the linked InfluxDB v2.1 reference page and review the metrics introduced in commit dece95d. Document the listed TSM compaction metrics for the InfluxDB v2.2 release, including their names and relevant Prometheus output details.

Written by the indexing model from the issue text.