Resolve fallback dns addrs during build

ts/types/DNSFallback.ts

@@ -0,0 +1,18 @@
+// Copyright 2024 Signal Messenger, LLC
+// SPDX-License-Identifier: AGPL-3.0-only
+
+import z from 'zod';
+
+export const DNSFallbackSchema = z.array(
+  z.object({
+    domain: z.string(),
+    endpoints: z.array(
+      z.object({
+        family: z.enum(['ipv4', 'ipv6']),
+        address: z.string(),
+      })
+    ),
+  })
+);
+
+export type DNSFallbackType = z.infer<typeof DNSFallbackSchema>;