Telemetry for Upgrades and CONNECT

[seanmonstar]

We now support both HTTP Upgrades (#1126) and CONNECT (#1200). They both make use of the HTTP sensors while the requests look like HTTP/1, and once the upgrade is complete, they convert into TCP proxies. That means no more HTTP sensors are used, but the transport sensors are still in place.

However, these are both probably significant enough to warrant emitting special events in our telemetry, so that users can see successful (and failed) HTTP Upgrades / CONNECT. Or maybe just Upgrades are sufficiently important.

A related question is whether something should be exposed in TAP.

[stale]

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[grampelberg]

@olix0r are we publishing metrics for these today?