added discord webhook target for valetudo notifications

[mstewart14]

so... I got a little OCD today and had a go at modifying the valetudo notification blueprint to provide input for a discord webhook, after I found the webhook service in HACS. I had to install it manually (not sure what's wrong there) but once installed and HA was restarted it worked and I got it working for a simple automation I built in the HA UI.
I have worked through the blueprint you built (which is awesome, thank you for doing this) and have managed to tack on the webhook target and payload without breaking the rest of the blueprint. Is this of interest to you? I've uploaded the file here.
Thank you again for the very helpful and instructive blueprint.
valetudo-notification-webhook-add-blueprint.zip