Enable Prow slack messages to SIG-etcd channel

[jberkus]

What would you like to be added?

Consider enabling the Prow plugin to message #sig-etcd or a new channel with Slack messages around PRs, merges, and test failures.

Why is this needed?

Per #16890, some contributors would like to add repo messages to Slack. Kubernetes slack does this via Prow plugins. If we want this, then that's what we need to enable.

This opens up the questions of:

1. Do we want repository activity messages in Slack?
2. Do we want them in the main #sig-etcd channel, or in a new channel?

Please discuss.

[liangyuanpeng]

Maybe k/k also have enabled the slack app in github org? Because I am listening to k/k event notifications through github slack. And this method allows users to subscribe to events from anywhere. In my case, I listen for k/k event notifications in my own slack channel.

See

[jberkus]

@liangyuanpeng are you saying that these notifications are from k/k, but are available in a different slack, as in not Kubernetes slack?

[liangyuanpeng]

are you saying that these notifications are from k/k, but are available in a different slack, as in not Kubernetes slack?

correct, It's working with https://slack.github.com/ .