Support additional output encodings

[JBurkinshaw]

The application currently supports HTML and JSON/GeoJSON output encodings for collection metadata and item data.

Add support for additional output encodings. This could potentially include GeoPackage, GML or flatgeobuf to name a few.

Careful consideration will need to be given if introducing dependencies like GDAL OGR. There is the potential to add complexity and inefficiencies to the application. There is some discussion of this in the readme.

[JBurkinshaw]

Consider encoding output in a streamable format like ndjson or GeoJSON text sequences (example given in spec for OGC API - Features - Part 1 )