* Re-did the mapping of DbAccountId so that we don't have to rely on derive...

* Re-did the mapping of DbAccountId so that we don't have to rely on derive macro FromJsonQueryResult that resulted in using JSON_TEXT in database column instead of VARCHAR
   * Tricky part I missed the first time was in impl of sea_orm::TryGetable::try_get_by where we should return Err TryGetError::Null in case the value is not present
   * Was otherwise throwing an exception whenever `parent` field (Option<DbAccountId>) was None when trying to persist the case in DB.