Refactor sync troubleshooting sections

What does this MR do?

I'm making a few updates to the Troubleshooting Geo synchronization and verification errors doc:

1. Reintroduce heading changes from !169476 (merged), which I think were lost when two docs were merged into this one
2. Put registry models in unordered list instead of plaintext code block
3. Clarify definition of "registry record"
4. Move Rails console info into each data type section, to make warning more obvious
5. Add note that Rails console should be opened on secondary site
6. Adjusted some phrasing about when features were introduced, for consistency
7. Fixed some placeholder variables that were not encased in <> (per Placeholder text)
8. Updated mention of issue for a feature that has since been merged, now using the History feature of docs platform

Related issues

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