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/admin-shared/package.json

@@ -0,0 +1,13 @@
+{
+  "name": "@medusajs/admin-shared",
+  "version": "0.0.0",
+  "types": "dist/index.d.ts",
+  "main": "dist/index.js",
+  "scripts": {
+    "build": "tsc"
+  },
+  "devDependencies": {
+    "typescript": "^5.3.3"
+  },
+  "packageManager": "yarn@3.2.1"
+}