add button labels

bubble-server/src/main/resources/message_templates/en_US/server/pre_auth/ResourceMessages.properties

@@ -288,6 +288,11 @@ err.dns.unknownError=Error connecting to DNS service
 err.storage.testFailed=Error testing connection to Storage service
 err.storage.unknownError=Error connecting to Storage service
 
+# New UI buttons
+button_label_sign_in=Sign In
+button_label_sign_up=Sign Up
+button_label_help=Help
+
 # Login/Registration/Forgot Password
 form_title_login=Login
 field_label_username=Username