Is your feature request related to a problem? Please describe.

When renaming a column with alembic, the generated SQL is not valid for BigQuery:

ALTER TABLE `schema`.`table` RENAME `old_name` TO `new_name`

BigQuery expects:

ALTER TABLE `schema`.`table` RENAME COLUMN `old_name` TO `new_name`

Describe the solution you'd like

Override the Alembic ColumnName op to generate the correct syntax.

Describe alternatives you've considered

Define the @compiles(ColumnName, "bigquery") in user code (outside this package)