feat: non-conflicting fetch instrumentation

[mrstork]

The current instrumentation patches global fetch which is import timing dependant and can conflict with other downstream patches and instrumentations. By subscribing to diagnostic channels, we are able to run alongside other instrumentations without risk of collisions.

• Changes the name of the span from fetch -> GET/POST/...
• Beyond ['HEAD', 'GET', 'POST', 'PUT', 'PATCH', 'DELETE'] the span will be named _OTHER
• Leverages startSpan instead of withActiveSpan since the span timing depends on separate messages
  • In other words, spans that were a result of http calls will no longer be nested under the http call (which I think makes more sense overall). Example below.

Before:

After: