ENH: Add max_results to `read_gbq`

[charlesdong1991]

For queries for which the purpose is to create/replace tables: CREATE OR REPLACE TABLE, if the table is huge, it will eat up a lot of memory currently using read_gbq.

And it turns out that since pandas-gbq==0.12.0, a new argument max_results was implemented to limit the number of rows in result dataframe for e.g. setting it to 0 for DDL queries, which will help save memory.

So it will be nice for pandas to add it for read_gbq as pandas-gbq does.

[JohnPaton]

I can take a swing at this!