[Desktop][Bug fix]: Stop target sessions before unauthenticating user session (#2891)

* add stopAll invocation to ipc handler

* trigger modal on both signout btns

* refactor invalidateSession fn

* fix application controller tests

* fix failing tests settings-card/user

* add test to Acceptance | authentication

* migrate electron dialog.showMessageBoxSync to Hds

* rename channel and tracked prop, consolidate cancel fns

* combine modals, add willDestroy, refactor

* test signout and close sessions modal

* address feedback

* refactor window.electron in authentication-test

* address feedback

* refactor: 💡 Fix failing tests

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Co-authored-by: Zhihe Li <zhihe.li@hashicorp.com>

addons/api/mirage/scenarios/ipc.js

@@ -246,6 +246,8 @@ export default function initializeMockIPC(server, config) {
     }
     pauseClientAgent() {}
     resumeClientAgent() {}
+    hasRunningSessions() {}
+    stopAll() {}
   }
 
   /**