feat: autogenerate vapid keys for push notifications (#3128)

* feat: Autogenerate push notification keys
* add vapid service class and remove pushkey model
* add spec for vapid service
* unset vapid env keys
* Unset VAPID_PRIVATE_KEY env variable

Co-authored-by: Sojan Jose <sojan@chatwoot.com>
Co-authored-by: Vishnu Narayanan <vishnu@chatwoot.com>

app/controllers/dashboard_controller.rb

@@ -28,6 +28,7 @@ class DashboardController < ActionController::Base
       'ANALYTICS_HOST'
     ).merge(
       APP_VERSION: Chatwoot.config[:version],
+      VAPID_PUBLIC_KEY: VapidService.public_key,
       ENABLE_ACCOUNT_SIGNUP: GlobalConfigService.load('ENABLE_ACCOUNT_SIGNUP', 'false')
     )
   end