[FE] Show custom label on register confirmation. Fix bug.

frontend/src/certs/NewRegister/ManualRegistration.tsx

@@ -54,6 +54,7 @@ export function ManualRegistration(props: {
         props.onAdd(data);
         // This is used to update & refresh the <SearchableSelect> component
         setCount((x) => x + 1);
+        setCustomLabel("");
     };
 
     const courseHasCustomLabel = () => {

frontend/src/certs/NewRegister/RegisterPreview.tsx

@@ -79,6 +79,7 @@ function Register(props: {courseId: number, date: string, customLabel: string, o
             >
                 <XIcon fill="var(--c-on-surface)" />
             </button>
+            {props.customLabel}
         </div>
     );
 }