Fix LDAP connection update on uniqueness change

[skalahonza]

Closes #18726

Details

• Update user and group LDAP sync to update_or_create connections keyed by (source, user/group) and refresh identifier when the uniqueness
  value changes.
• Prevents duplicate (user, source)/(group, source) constraint errors after remapping ldap_uniq/object_uniqueness_field.

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Checklist

• Local tests pass (ak test authentik/)
• The code has been formatted (make lint-fix)

If an API change has been made

• The API schema has been updated (make gen-build)

If changes to the frontend have been made

• The code has been formatted (make web)

If applicable

• The documentation has been updated
• The documentation has been formatted (make docs)

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