server: generate reports

[zeroXbrock]

Is your feature request related to a problem? Please describe.

I can't generate a report from a spam run via the JSON-RPC API, but I reeeeeallly want to.

Describe the solution you'd like

• add an endpoint to the RPC server: report({session_id, format}) that generates a report spanning every run_id in the session's DB
  • acceptable format: "json" and "html"
  • the endpoint should start generating the report, then return immediately with the link to the report (e.g. "http://localhost:3000/report/321123.json")
  • reports are saved to a temp directory when completed
• add an endpoint to the REST server (the same one that hosts the SSE streams) to host the reports: /report/{session_id}.{suffix}
• delete the temp directory before shutting down the server