Added config to change Gravatar URL

.env.example

@@ -61,6 +61,11 @@ DISCORD_APP_SECRET=false
 
 # External services such as Gravatar and Draw.IO
 DISABLE_EXTERNAL_SERVICES=false
+# Default GRAVATAR_URL set to Gravatar service
+GRAVATAR_URL=false
+# To use a different service to get user's avatar like libravatar
+# Possible placeholders: %{hash} %{size} %{email}
+#GRAVATAR_URL=https://seccdn.libravatar.org/avatar/%{hash}?s=%{size}&d=identicon
 
 # LDAP Settings
 LDAP_SERVER=false