Added source for join context (#3116)

## Description:

Added source for join context

## 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:

w.o.n

src/client/Matchmaking.ts

@@ -231,6 +231,7 @@ export class MatchmakingModal extends BaseModal {
         detail: {
           gameID: this.gameID,
           clientID: getClientIDForGame(this.gameID),
+          source: "matchmaking",
         } as JoinLobbyEvent,
         bubbles: true,
         composed: true,