Turnstile: require token before joining a multiplayer game (#2572)

When user tries to join either a public or private multiplayer game, the
turnstile callback is triggered, and the turnstile token is passed to
the server when joining a game.

## Please complete the following:

- [x] I have added screenshots for all UI updates
- [x] I process any text displayed to the user through translateText()
and I've added it to the en.json file
- [x] I have added relevant tests to the test directory
- [x] I confirm I have thoroughly tested these changes and take full
responsibility for any bugs introduced

## Please put your Discord username so you can be contacted if a bug or
regression is found:

evan

tests/util/TestServerConfig.ts

@@ -4,6 +4,12 @@ import { GameMapType } from "../../src/core/game/Game";
 import { GameID } from "../../src/core/Schemas";
 
 export class TestServerConfig implements ServerConfig {
+  turnstileSiteKey(): string {
+    throw new Error("Method not implemented.");
+  }
+  turnstileSecretKey(): string {
+    throw new Error("Method not implemented.");
+  }
   enableMatchmaking(): boolean {
     throw new Error("Method not implemented.");
   }