Feature Request: add option overwrite to ref.to_table(...)

[frafra]

.create(...)/.to_table(...) allow persisting a relationship on a database table when using Python, but there is no option to replace the existing one.

[jokasimr]

It would be neat if there was also a way to create a table / view with create if not exists from python.

One option is:

• If replace=True the table should be created with CREATE OR REPLACE.
• If replace=False the table should be created with plain CREATE.
• If replace='if not exists' the table should be created with CREATE IF NOT EXISTS.

[leostimpfle]

Related #525 and #430