Add translation keys for welcome page (#1499)

* Begin Work

* WIP

* Add long title key

* Finish work (for now)

* Fix lint error

* Add continue button key

* Make continue button key generic

utils/common-messages.ts

@@ -7,6 +7,10 @@ export const commonMessages = defineMessages({
     id: 'button.cancel',
     defaultMessage: 'Cancel',
   },
+  continueButton: {
+    id: 'button.continue',
+    defaultMessage: 'Continue',
+  },
   dateAtTimeTooltip: {
     id: 'tooltip.date-at-time',
     defaultMessage: '{date, date, long} at {time, time, short}',