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/HostLobbyModal.ts

@@ -655,6 +655,7 @@ export class HostLobbyModal extends BaseModal {
             detail: {
               gameID: this.lobbyId,
               clientID: this.lobbyCreatorClientID,
+              source: "host",
             } as JoinLobbyEvent,
             bubbles: true,
             composed: true,