allow *yaml* in ouput

[JohnRDOrazio]

Currently, the API has a preference for JSON output, with some support for XML output and ICS output. However nowadays another popular data exchange format is YAML. We should enable a request for Content Type application/yaml.

This will require enabling the pecl extension yaml-emit on the server and implementing a minimum amount of logic to allow the transform on output.

[JohnRDOrazio]

first step taken, pecl package is now installed on the server!

[JohnRDOrazio]

apparently yaml_emit cannot directly handle PHP objects, only associative arrays (see php/pecl-file_formats-yaml issue #70). So unless that's ever a thing, we'll just have to json_decode(json_encode($output),true) to get an associative array, and then yaml_emit from there.

[JohnRDOrazio]

Implemented in commits c734a38...82bbf7c !

[JohnRDOrazio]

and added application/yaml to the OpenAPI schema in commit 82bbf7c...a359952 !
This issue is now complete!

[JohnRDOrazio]

yaml validation is now a thing too, in the litcal-tests interface! Implemented validation here in LitCalHealth and added the option in the tests interface.