API method to return profiling data as raw JSON

[narqo]

To move forward with web UI #107 profefe needs its querier (part of profefe-collector) to provide a way of getting the profiling data as raw JSON (TBD full profile or samples only?).

Something like /api/0/profiles/<id>?format=json could work as a good start.

As for the JSON schema, it could be a pprof specific, i.e. raw parsed pprof profile (json-marshalled); or something generic, i.e

• W3C draft for JS self-profiling API defines ProfilerTrace schema
  • https://wicg.github.io/js-self-profiling/#the-profilertrace-dictionary
• the schema used by speedscope
  • https://github.com/jlfwong/speedscope/blob/master/src/lib/file-format-spec.ts
  • https://www.speedscope.app/file-format-schema.json
• the schema used in Firefox Profiler
  • https://github.com/firefox-devtools/profiler/blob/main/src/types/profile.js
• other candidates?