Make threads disabled by default (#9810)

* Make threads disable by default

* restore e2ee tests

* fix threads e2e spec for beta joining

cypress/e2e/polls/polls.spec.ts

@@ -77,6 +77,7 @@ describe("Polls", () => {
     };
 
     beforeEach(() => {
+        cy.enableLabsFeature("feature_threadstable");
         cy.window().then((win) => {
             win.localStorage.setItem("mx_lhs_size", "0"); // Collapse left panel for these tests
         });