add: allow supporters to upload gif avatars/banners

crates/core/src/model/mod.rs

@@ -43,6 +43,7 @@ pub enum Error {
     UsernameInUse,
     TitleInUse,
     QuestionsDisabled,
+    RequiresSupporter,
     Unknown,
 }
 
@@ -63,6 +64,9 @@ impl Display for Error {
             Self::UsernameInUse => "Username in use".to_string(),
             Self::TitleInUse => "Title in use".to_string(),
             Self::QuestionsDisabled => "You are not allowed to ask questions there".to_string(),
+            Self::RequiresSupporter => {
+                "Only site supporters can upload GIF files as their avatar/banner".to_string()
+            }
             _ => format!("An unknown error as occurred: ({:?})", self),
         })
     }