Add GC run stats

[LesnyRumcajs]

Summary

Docs should provide information on Forest disk usage + the actual effects on GC with real numbers. Run Forest for a week, collect necessary information from the system and compile into a report that could be embedded into the user docs.

Completion Criteria

• Docs are updated with node disk usage with GC enabled; how much disk space it consumes, how often the GC kicks in, the GC effect on disk usage etc.
• The above is done for calibnet
• and mainnet

Additional Links & Resources

Migrated from https://github.com/ChainSafe/forest-docs-v2/issues/109