Killing collector with ctrl + c leads to "phantom collector"

[agardnerIT]

When everything is running (server, UI and a collector), kill a collector with ctrl + c.

Sometimes (but not every time) the collector will stop and the server never receives notification thus Prometheus (https://localhost:4320/metrics) shows:

# HELP connected_agents The number of currently connected agents
# TYPE connected_agents gauge
connected_agents 1.0

And the UI shows:

But there really is no collector connected.

I believe this behaviour is due to this and this PR purports to resolve the issue.

I don't want to hack around this behaviour, especially since the collector doesn't seem to adhere to the OpAMP spec.

I'm marking this as a known upstream issue and if / when that's fixed, we can revisit this bug (hopefully it is then simply to solve by listening for a proper "disconnect" message and decrementing lists and counters).