fix: Allow Instructors to create prospect chats (#979)

Co-authored-by: Jonas Wilms <[email protected]>

graphql/chat/mutations.ts

@@ -86,7 +86,7 @@ export class MutateChatResolver {
     }
 
     @Mutation(() => String)
-    @Authorized(Role.PUPIL)
+    @Authorized(Role.PARTICIPANT, Role.INSTRUCTOR)
     async prospectChatCreate(@Ctx() context: GraphQLContext, @Arg('instructorUserId') instructorUserId: string, @Arg('subcourseId') subcourseId: number) {
         const { user: prospectUser } = context;
         const instructorUser = await getUser(instructorUserId);