This commit makes the remote diagnostics enabled by default, which is
a useful feature when debugging cloudflared issues without manual intervention from users.
Users can still opt-out by disabling the feature flag.
With the new flag --management-diagnostics (an opt-in flag)
cloudflared's will be able to report additional diagnostic information
over the management.argotunnel.com request path.
Additions include the /metrics prometheus endpoint; which is already
bound to a local port via --metrics.
/debug/pprof/(goroutine|heap) are also provided to allow for remotely
retrieving heap information from a running cloudflared connector.