SSR: Added new option to complete env example file

Author: ssddanbrown

.env.example.complete

@@ -359,6 +359,15 @@ ALLOWED_IFRAME_HOSTS=null
 # Current host and source for the "DRAWIO" setting will be auto-appended to the sources configured.
 ALLOWED_IFRAME_SOURCES="https://*.draw.io https://*.youtube.com https://*.youtube-nocookie.com https://*.vimeo.com"
 
+# A list of the sources/hostnames that can be reached by application SSR calls.
+# This is used wherever users can provide URLs/hosts in-platform, like for webhooks.
+# Host-specific functionality (usually controlled via other options) like auth
+# or user avatars for example, won't use this list.
+# Space seperated if multiple. Can use '*' as a wildcard.
+# Values will be compared prefix-matched, case-insensitive, against called SSR urls.
+# Defaults to allow all hosts.
+ALLOWED_SSR_HOSTS="*"
+
 # The default and maximum item-counts for listing API requests.
 API_DEFAULT_ITEM_COUNT=100
 API_MAX_ITEM_COUNT=500