adds support for querying Redshift Serverless clusters

[ivica-k]

Adds support for querying Redshift Serverless clusters using the RedshiftDataOperator. Serverless clusters require the workgroup_name to be specified and do not require the cluster_identifier.

Closes #32280

Tested with this DAG:

from airflow import DAG
from airflow.providers.amazon.aws.operators.redshift_data import RedshiftDataOperator

default_args = {
    "start_date": "2023-03-01",
}

dag = DAG(
    "test_redshift_serverless",
    default_args=default_args,
    schedule="0 0 1,15 * *",
    catchup=False
)

try:
    rd = RedshiftDataOperator(
        task_id="run_this",
        dag=dag,
        database="dev",
        workgroup_name="wg-ivica",
        sql="select current_user;",
        aws_conn_id="aws_default",
        wait_for_completion=True,
        return_sql_result=True
    )

    rd
    
except Exception as msg:
    print(msg)

and with using my personal AWS credentials, the result showed that the current user is IAM:ikolenkas, which is correct.

{
	"ColumnMetadata": [{
		"isCaseSensitive": true,
		"isCurrency": false,
		"isSigned": false,
		"label": "current_user",
		"length": 0,
		"name": "current_user",
		"nullable": 1,
		"precision": 63,
		"scale": 0,
		"schemaName": "",
		"tableName": "",
		"typeName": "bpchar"
	}],
	"Records": [
		[{
			"stringValue": "IAM:ikolenkas"
		}]
	],
	"TotalNumRows": 1,
	"ResponseMetadata": {
		"RequestId": "6ec07443-80c7-4681-823d-fa7689e85e7a",
		"HTTPStatusCode": 200,
		"HTTPHeaders": {
			"x-amzn-requestid": "6ec07443-80c7-4681-823d-fa7689e85e7a",
			"content-type": "application/x-amz-json-1.1",
			"content-length": "289",
			"date": "Sun, 23 Jul 2023 13:06:12 GMT"
		},
		"RetryAttempts": 0
	}
}

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[Lee-W]

nitpick: i think we should reorder the docstring as well

[ivica-k]

Absolutely :) addressed in 71bea87

[Lee-W]

nitpick: same here

[ivica-k]

Same here: addressed in 71bea87 :)

[Lee-W]

not sure whether this will need to be reordered

[ivica-k]

Also not sure, but for consistency addressed in 71bea87

[vincbeck]

Besides the nits mentioned by @Lee-W , it looks good to me :) Good job!