[docs] Update dbv3 content (#19867)

## Description 

DBv3 is now on Mainnet. Makes the sentence removed somewhat pointless.

## Test plan 

👀 

---

## Release notes

Check each box that your changes affect. If none of the boxes relate to
your changes, release notes aren't required.

For each box you select, include information after the relevant heading
that describes the impact of your changes that a user might notice and
any actions they must take to implement updates.

- [ ] Protocol: 
- [ ] Nodes (Validators and Full nodes): 
- [ ] Indexer: 
- [ ] JSON-RPC: 
- [ ] GraphQL: 
- [ ] CLI: 
- [ ] Rust SDK:
- [ ] REST API:

docs/content/snippets/deepbook.mdx

@@ -1,18 +1,33 @@
+import React, { useState, useEffect } from "react";
 import { useLocation } from "@docusaurus/router";
 import useGlobalData from '@docusaurus/useGlobalData';
 import Link from '@docusaurus/Link';
 
 export function DBV() {
+  const [showNotice, setShowNotice] = useState(false);
   const location = useLocation();
   const isV3 = location.pathname.includes("v3");
+  useEffect(() => {
+    const currentDate = new Date();
+    const endDate = new Date("2024-10-31T23:59:59");
+    // Don't show after October; remove if still here
+    if (currentDate <= endDate) {
+      setShowNotice(true);
+    } else {
+      setShowNotice(false);
+    }
+  }, []);
+
 
   function DBLink() {
     return <Link href={isV3 ? "/standards/deepbookv2" : "/standards/deepbookv3"}>DeepBook{isV3 ? "V2" : "V3"} docs</Link>
   }
 
   return (
     <>
-      This documentation is for <b>version {isV3 ? "3" : "2"}</b> of DeepBook. DeepBook{isV3 ? "V3" : "V2"} is currently available in {isV3 ? "Devnet and Testnet" : "Mainnet"}. For documentation on version {isV3 ? "2" : "3"} of DeepBook, see <DBLink />.  
+      { showNotice ? <p>DeepBookV3 is now available on Mainnet!</p> : "" }
+      <p>This documentation is for <b>version {isV3 ? "3" : "2"}</b> of DeepBook. For documentation on version {isV3 ? "2" : "3"} of DeepBook, see <DBLink />.
+      </p> 
     </>
   )