implement waitlist for non-en-US core add-on page

[rhelmer]

There's a comment in the non-en-US splash page that the core add-on shows, we should implement this so users that are ineligible are offered the waitlist:

rally-core-addon/src/routes/non-eligible-splashes/NonUSUser.svelte

Lines 86 to 90 in 9ab7802

	<!-- uncomment out this block and update the link when we have the waitlist available -->
	<!-- <div class="waitlist">
	<a target="_blank" rel="noopener noreferrer" href="__BASE_SITE__/waitlist/">Join the Waitlist
	<ExternalLink /></a>
	</div> -->