Refactor RDS queries to use new simplified JSON response functionality.

[sharkinsspatial]

Many of our current Lambda's which query the RDS Data API have difficult to read / unclear response parsing code https://github.com/NASA-IMPACT/hls-orchestration/blob/dev/lambda_functions/process_landsat_mgrs_incompletes.py#L33-L39 due to the RDS Data API response structure. AWS has released updated functionality to allow simpler direct response bodies
https://aws.amazon.com/about-aws/whats-new/2022/04/amazon-rds-data-api-sql-json-string/