Pass-through API route should support gzipped carto responses

[timwis]

@andrewbt discovered that carto gzips large payloads, and AWS' API Gateway doesn't seem to support that in its http proxy / pass-through. Thought I'd create a separate issue since it's a bit different from simply standing up the pass-through API via cloudformation code.

[andrewbt]

Resolved this via adding an "Accept-Encoding" header with value 'identity' to the API gateway Integration Request.

Testable here: https://zsp6egcjhf.execute-api.us-east-1.amazonaws.com/dev/carto/v2/sql?q=select * from indego_stations where ST_DWITHIN(the_geom::geography, ST_GeographyFromText('POINT(-75.1636 39.9524)'),500)

Screenshots: