Improve error handling

[declark1]

Description

Improve error handling:

• Determine the appropriate level of error granularity and add variants to capture context or use anyhow::Error (with it's Context trait)
  • e.g. rather than returning Error::ReqwestError, we probably want something like Error::Detector("request timed out")
• Ensure errors flow up cleanly from orchestrator tasks, we should not be using Result::unwrap()
• Properly convert Error variants into suitable http::StatusCode (with a message for context) to return to caller from handler methods