HDDS-10110. Use RocksDB key count estimates instead of OM metrics file.

[errose28]

What changes were proposed in this pull request?

• Use RocksDB column family key count estimates to initialize OM metrics that need to survive restarts or be updated on snapshot install.
• Remove OM metrics json file
• Clarify usage of existing OM count metrics. Previous definitions of these metrics were inconsistent.
  • numKeys: The number of entries in OBS or Legacy buckets, regardless of the value of ozone.om.enable.filesystem.paths.
  • numDirs: The number of directories in FSO buckets.
  • numFiles: The number of files in FSO buckets.

See the Jira description for history and details of changes to these OM metrics. With this solution, all metrics should be corrected on OM restart without repairs required. Opening this as a draft PR to get comments on the approach while tests are being finished.

What is the link to the Apache JIRA

HDDS-10110

How was this patch tested?

• [ ] WIP