## Context
Fix wrong unique index on user email as we don't want an index on
email/deletedAt but a partial on a where condition on deletedAt. This
should enforce email unicity excluding the ones that have a deletedAt
## Test
Run
```sql
SELECT email, COUNT(*) as duplicate_count
FROM core."user"
WHERE "deletedAt" IS NULL
GROUP BY email
HAVING COUNT(*) > 1
ORDER BY duplicate_count DESC;
```
to check duplicates before running the migration
c993f2de0b