Webhooks plugin for Kirby 3

Hi there, the plugin is now available to install via composer as well, so I have officially put it out of beta :wink:

@texnixe This is me pinging you because this could go to the next Kosmos issue? There is also this plugin now though, so I might have to figure out the naming first …

// Update:
I have renamed the plugin to avoid confusion :slight_smile: @texnine This should be ready to go I hope.