Consider supporting a --dry-run option for targets

[kgpayne]

During development and testing of targets, it would be useful to have access to a dry-run flag. In dry-run mode the target would operate as normal except without making any write actions. E.g.

    def bulk_insert_records(
        self,
        full_table_name: str,
        schema: dict,
        records: Iterable[Dict[str, Any]],
    ) -> Optional[int]:
        """Bulk insert records to an existing destination table.

        The default implementation uses a generic SQLAlchemy bulk insert operation.
        This method may optionally be overridden by developers in order to provide
        faster, native bulk uploads.

        Args:
            full_table_name: the target table name.
            schema: the JSON schema for the new table, to be used when inferring column
                names.
            records: the input records.

        Returns:
            True if table exists, False if not, None if unsure or undetectable.
        """
        insert_sql = self.generate_insert_statement(
            full_table_name,
            schema,
        )
        if isinstance(insert_sql, str):
            insert_sql = sqlalchemy.text(insert_sql)

        conformed_records = (
            [self.conform_record(record) for record in records]
            if isinstance(records, list)
            else (self.conform_record(record) for record in records)
        )
        self.logger.info("Inserting with SQL: %s", insert_sql)
        if not self.dry_run:  # only actually upload records if not in dry-run mode
            self.connector.connection.execute(insert_sql, conformed_records)
        return len(conformed_records) if isinstance(conformed_records, list) else None