feat(tournament): enable external participation in tournaments

- Updated tournamentService to allow external participants by setting allowsExternal to true.
- Adjusted frontend TournamentTab component to reflect the change, enabling external participation for mini championships.

backend/services/tournamentService.js

@@ -739,7 +739,7 @@ class TournamentService {
                 numberOfGroups: 1,
                 advancingPerGroup: 1,
                 winningSets: sets,
-                allowsExternal: false,
+                allowsExternal: true,
                 miniChampionshipYear: Y
             }, { transaction });