Support setting reservation on a job

[carolkng]

It seems like newer versions of the golang google api versions (namely, v0.227.0) support the addition of a Reservation string in JobConfiguration to dynamically set the reservation assignment on a job.

It seems like there is another method of dynamically setting the reservation by adding this line to a query (documented here):

SET @@reservation = 'reservation_id'; 
-- query below will use the specified reservation above
SELECT 'placeholder_value';

which also works with the BigQuery API, but isn't compatible with the driver due to the @s required to set the reservation variable.

cc: @adranwit -- do you have a preference for which approach might be preferred here?

• amending the check query param + query preparation logic to accept the @@reservation variable as-is without substitution
• upgrading the underlying google go api client version to one that supports setting reservation on job configuration