Potential PostgreSQL result handler improvements #1755

For consideration.

1. Create table error handler

If self._client.create_table below throws an exception, there are a couple of cases we can provide a more informative error message.

        try:
            _ = clients.get_ibis_table(self._client, schema_name, table_name)
            # Do nothing, the table exists.
        except sqlalchemy.exc.NoSuchTableError:
            self._client.create_table(table_name, schema=RESULTS_TABLE_SCHEMA)

• psycopg2.errors.InvalidSchemaName then either the schema does not exist or, more likely, we are missing the USAGE privilege. We can give the user some clues in the error message. GRANT USAGE ON SCHEMA ...
• psycopg2.errors.InsufficientPrivilege then we are missing the CREATE privilege. GRANT CREATE ON SCHEMA ...

2. Result table

Should we create some default indexes on the results table?

• run_id
• source_table_name