validate file sink when creating instead of when actually sinking data

[lmatz]

dev=> CREATE TABLE t (k INT);
CREATE_TABLE
dev=> CREATE SINK file_sink
dev-> FROM
dev->   t
dev-> WITH
dev-> (
dev(>   connector = 's3',
dev(>   s3.region_name = 'us-east-1',
dev(>   s3.bucket_name = 'test',
dev(>   s3.path = '',
dev(>   s3.file_type = 'parquet',
dev(>   type = 'append-only',
dev(>   force_append_only='true'
dev(> ) FORMAT PLAIN ENCODE PARQUET(force_append_only='true');
CREATE_SINK

Everything shows ok until

insert into t values (1);

then shows in the log that:

ERROR risingwave_connector::sink::file_sink::s3: secret access key of aws s3 is not set, bucket  test

[lmatz]

#18159