This is probably conceptually nicer although isn't quite as nice in
the jaeger / stalk UI.
Also this may no loger work with the posthog exporter (unsure what it
will do with events on spans).
Adds an nginx in front of the query endpoint so we can use stalk
without faffing with browser extension to bypass CORS.
Also make the spans correctly have the call membership span as parent,
which they didn't because we hadn't set the span at the point we made
the context.
