Emit an event when the informer reconnects the watch feed

[dominykas]

My primary use case for this is just logging - there's an issue #596 about the watcher silently stopping and this might help debug the problem.

We're already operating a controller written in Node.js, and we've spotted similar issues - having some logs around the reconnection (and having them missing when things go south) has helped in trying to at
least determine a rough range of time when the problems started occurring (fwiw - it seems to be related to master node rotation, although not easily reproducible).

It would be nice if Informer was able to emit something like connected each time it restarts the watcher?

[brendandburns]

Sure. One other thing that we should probably do is add Prometheus metrics so that you can monitor them in addition to monitoring the logs.