docs: update .env.sample to clarify WEBHOOK_URL protocol support

Author: kastov

.env.sample

@@ -58,7 +58,7 @@ METRICS_PASS=admin
 
 ### WEBHOOK ###
 WEBHOOK_ENABLED=false
-### Only https:// is allowed
+### Can be https:// or http://
 WEBHOOK_URL=https://webhook.site/1234567890
 ### This secret is used to sign the webhook payload, must be exact 64 characters. Only a-z, 0-9, A-Z are allowed.
 WEBHOOK_SECRET_HEADER=vsmu67Kmg6R8FjIOF1WUY8LWBHie4scdEqrfsKmyf4IAf8dY3nFS0wwYHkhh6ZvQ