Add handler for rocketchat handler

[kanzifucius]

Adding a rocketchat handler

[mfilotto]

Any update on this one ?

[judexzhu]

We're using RocketChat in our company, wish we could have this handler soon.

[judexzhu]

@mfilotto I used the webhook with Rocketchat

Turns out it's pretty good, you might try it too.

But I have to config each webhook for multiple clusters

[julianrubisch]

@judexzhu do you have some details on how you configured the kubewatch webhook for rocketchat? I'm getting invalid_auth here...