Add disclaimer slot to Checkout component

Introduced a new slot named "disclaimer" in the Checkout component to allow for additional user-defined content. Updated relevant files to demonstrate the usage of this new slot, enabling a flexible and modular design. This enhancement allows for the inclusion of important notices or legal disclaimers in the checkout process.

Author: kazuyoshi80

example/Checkout.astro

@@ -25,7 +25,11 @@ const payload = toUtf8Bytes('tier-1')
 		uiMode="embed"
 		{...props}
 	>
-		<div class="opacity-50" slot="checkout:disclaimer">We strictly prohibit any unauthorized reproduction, reprinting, reuse, or modification of any part or all of the content (images, text, etc.) published on this site</div>
+		<div class="opacity-50" slot="checkout:disclaimer">
+			We strictly prohibit any unauthorized reproduction, reprinting, reuse, or
+			modification of any part or all of the content (images, text, etc.)
+			published on this site
+		</div>
 	</Checkout_>
 </div>