feat(admin-*,dashboard): add dashboard i18n extensions (#13763)

* virtual i18n module

* changeset

* fallback ns

fallback to the default "translation" ns if the key isnt found. Allows to use a single "useTranslation("customNs")" hook for both custom and medusa-provided keys

* simplify merges

* optional for backward compat

* fix HMR

* fix generated deepMerge

* test

packages/admin/admin-vite-plugin/src/i18n/helpers.ts

@@ -0,0 +1,15 @@
+import { crawl } from "../utils"
+
+/**
+ * Get i18n index files from sources
+ * Looks for src/admin/i18n/index.ts in each source
+ */
+export async function getI18nIndexFilesFromSources(
+    sources: Set<string>
+): Promise<string[]> {
+    return (await Promise.all(
+        Array.from(sources).map(async (source) =>
+            crawl(`${source}/i18n`, "index", { min: 0, max: 0 })
+        )
+    )).flat()
+}