Follow-up to #2301
Updates the 0039 migration to ensure collection slugs and names are
unique by:
- Removing all indexes
- Setting `slug` to random value
- Adding unique index to `slug` field.
- Attempting to set slug from name using `slug_from_name()`
- If rejected due to duplicate, append `-<counter>` at end of slug. Also
update name with ` <counter>`.
- Now that names should also be unique, add unique index on name field.
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Co-authored-by: Tessa Walsh <tessa@bitarchivist.net>
