Fix duplicate copy warning alert (Azure-Samples#230)

* Fix duplicate copy warning alert

- It was being added to the whole page everytime an answer was returned
- This meant that if **any** content on the page was copied the alert was
  being shown multiple times based on how many answers there had been
- This change will mean the alert will now only be shown when an answer
  is copied and only once

Required by Azure-Samples#215

* Address review comments

code/app/frontend/src/components/Answer/Answer.tsx

@@ -14,15 +14,19 @@ import supersub from 'remark-supersub'
 interface Props {
     answer: AskResponse;
     onCitationClicked: (citedDocument: Citation) => void;
+    index: number;
 }
 
 export const Answer = ({
     answer,
-    onCitationClicked
+    onCitationClicked,
+    index,
 }: Props) => {
     const [isRefAccordionOpen, { toggle: toggleIsRefAccordionOpen }] = useBoolean(false);
     const filePathTruncationLimit = 50;
 
+    const messageBoxId = "message-" + index;
+
     const parsedAnswer = useMemo(() => parseAnswer(answer), [answer]);
     const [chevronIsExpanded, setChevronIsExpanded] = useState(isRefAccordionOpen);
 
@@ -57,15 +61,16 @@ export const Answer = ({
         const handleCopy = () => {
             alert("Please consider where you paste this content.");
         };
-        document.addEventListener("copy", handleCopy);
+        const messageBox = document.getElementById(messageBoxId);
+        messageBox?.addEventListener("copy", handleCopy);
         return () => {
-            document.removeEventListener("copy", handleCopy);
+            messageBox?.removeEventListener("copy", handleCopy);
         };
     }, []);
 
     return (
         <>
-            <Stack className={styles.answerContainer}>
+            <Stack className={styles.answerContainer} id={messageBoxId}>
                 <Stack.Item grow>
                     <ReactMarkdown
                         remarkPlugins={[remarkGfm, supersub]}

code/app/frontend/src/pages/chat/Chat.tsx

@@ -302,6 +302,7 @@ const Chat = () => {
                               : [],
                         }}
                         onCitationClicked={(c) => onShowCitation(c)}
+                        index={index}
                       />
                     </div>
                   ) : null}