Expand information about infobox in webhook config

[tw-martijn]

I was doing a lot of testing w.r.t. displaying errors when things have not been fully configured on a customer’s account on our end. I noticed:

1. it seems like the infoboxes no longer use icons (I think they did before?) and only apply styling. E.g. bg-warning and bg-danger classess.
2. it is possible to use infoboxes as a replacement for the error type field by making sure required is set to true. Doing that will disable the “Add trigger” button. This way some messages can use warning styling but still block the end-user from creating the trigger in their job.

[tw-martijn]

I was inspired to test the required trick after seeing the example form-config-error from the example-webhook repository. That one uses the hidden type, but that seems unnecessary when the error can be rendered to the end-user with an infobox.