Compatible with CockroachDB function `TO_DATE`

[intech]

In file /superset/db_engine_specs/cockroachdb.py need to add the override method:

superset/superset/db_engine_specs/postgres.py

Lines 332 to 333 in fd3030f

	if isinstance(sqla_type, Date):
	return f"TO_DATE('{dttm.date().isoformat()}', 'YYYY-MM-DD')"

And change to the TO_CHAR function:

return f"TO_CHAR('{dttm.date().isoformat()}', 'YYYY-MM-DD')" 

[rusackas]

I'm not sure if this is still an issue in current versions of Superset (3.x). If it is, we can re-open this, or feel free to open a new issue with updated context and a reproducible case using example data. We're no longer supporting Superset 2.x or prior, and it's been a while since this thread saw any activity, so I'm closing this as stale.