Add support for compression (e.g. gzip)

[brylie]

With recent changes, we are looking at allowing requests to be made with a considerable amount of data (namely lists of itinerary objects with arbitrary fields.) One performance optimization for large payloads is to use gzip, or similar, compression.

Task

• determine how to define that the API supports compression
• add necessary changes to specification and in code to support compression

Resources

• discussion about defining compression in OpenAPI Specification
• GZIP compression might be best added at the HTTP server level
• AWS Enabling payload compression for an API