Provide more detailed documentation about Che telemetry implementation

[davidfestal]

• Provide complete documentation about:
  • the design + Java implementation of Che workspaces telemetry
  • the design of Che telemetry related to client-side end2end flow
  • The various parts of Che telemetry work that are stored in Woopra itself (trigger, segments, definition of official reports)
• Provide a link to this additional documentation into the HK dev guide.

[ibuziuk]

Closing in favour of eclipse-che/che#16715