Chore: Make argument specification consistent

[talagluck]

Description

Currently, we have two different ways of specifying arguments/options in GlareDB, = and =>. The following example fails with = and works with =>

SELECT * FROM read_parquet('s3://glaredb-sandbox/f55363e2587849bcb25c057be706c69d-0.parquet',
    my_aws_creds,
    region='us-east-2');

But this example only works with = and fails with =>

CREATE CREDENTIALS my_aws_creds PROVIDER aws
     OPTIONS (
         access_key_id = 'my_key',
         secret_access_key = 'my_secret_key'
     );

Ideally, we would be able to use = in all of these cases. If there are shortcomings with the parser, we could instead use => in all cases. But having these be inconsistent is confusing.