Expose all output formats on the same HTTP endpoint

[c10l]

It would be good to be able to run the HTTP endpoint once and let the clients pick the output format, either via HTTP headers or a URL parameter, e.g. http://localhost:8080/healthz?format=json

That way you'd need to run only one endpoint and use it for machine-friendly healthchecks (JSON), human validation (rspecish), CI jobs (JUnit), etc.

[pysysops]

Interesting idea... This might not be too difficult to do.

[aelsabbahy]

Not overly complex, but caching will have to be refactored a little bit.

[aelsabbahy]

closed by #609