Category changes:
- Fix existing_id handling to check if string is numeric before using as
site setting name. Previously numeric strings like '3' would cause
errors when passed to SiteSetting.get().
Group changes:
- Add existing_id support for groups, allowing mapping imported groups
to existing Discourse groups by ID or name.
- When existing_id is specified, skip group creation and map imported_id
to the existing group.
This enables importing users into pre-existing groups without creating
duplicates, similar to category existing_id functionality.
Co-authored-by: root <root@migrations02.sjc4.discourse.cloud>
Ruben Oussorenandroot
ed28dd9cfe