Feature Requests Allow placeholder in webhooks URL

URLs for webhooks should have the option of inserting placeholders in the url.

E.g. the push service Pushover uses a url like: https://api.pushover.net/1/messages.json?user=xxx&token=yyy&message=Website%20Down to send a push message to my phone.

I would like to specify the message, but the url would need placeholders which get replaced by updown.io.

E.g. like this: https://api.pushover.net/1/messages.json?user=xxx&token=yyy&message={{description}} to use the webhooks data entry description.