chore: move next admin packages to core repo (#5983)

**What**
- Move packages for `next` version of admin to core repo

**Other**
- Since this PR introduces packages that depend on Vite 5, it also introduces @types/node@^20. We have never had a direct dependency on the types package for Node, and as far as I can see that has resulted in us using the types from Node.js@8, as those are a dependency of one of our dependencies. With the introduction of @types/node@^20, two of our packages had TS errors because they were using the NodeJS.Timer type, which was deprecated in Node.js@14. We should add specific @types/node packages to all our packages, but I haven't done so in this PR to keep it as clean as possible.
- Q: @olivermrbl I've added the new packages to the ignore list for changeset, is this enough to prevent them from being published?

packages/admin-next/dashboard/src/module.d.ts

@@ -0,0 +1,39 @@
+declare module "medusa-admin:widgets/*" {
+  const widgets: { Component: () => JSX.Element }[]
+
+  export default {
+    widgets,
+  }
+}
+
+declare module "medusa-admin:routes/links" {
+  const links: { path: string; label: string; icon?: React.ComponentType }[]
+
+  export default {
+    links,
+  }
+}
+
+declare module "medusa-admin:routes/pages" {
+  const pages: { path: string; file: string }[]
+
+  export default {
+    pages,
+  }
+}
+
+declare module "medusa-admin:settings/cards" {
+  const cards: { path: string; label: string; description: string }[]
+
+  export default {
+    cards,
+  }
+}
+
+declare module "medusa-admin:settings/pages" {
+  const pages: { path: string; file: string }[]
+
+  export default {
+    pages,
+  }
+}