feat(admin-bundler,admin-vite-plugin,medusa): Add support for loading Admin Extensions from plugins (#10869)

Should not be merged before https://github.com/medusajs/medusa/pull/10895

**What**
- Introduces a new `plugin` command to `admin-bundler`, currently not used anywhere but will be called from `medusa build:plugin`
- Discovers plugins with extensions and add passes the to `admin-vite-plugin`.
- Updates `admin-vite-plugin` so its able to read built admin extensions.

Resolves CMRC-830, CMRC-839

packages/admin/admin-bundler/package.json

@@ -32,6 +32,7 @@
     "@vitejs/plugin-react": "^4.2.1",
     "autoprefixer": "^10.4.16",
     "compression": "^1.7.4",
+    "glob": "^11.0.0",
     "postcss": "^8.4.32",
     "tailwindcss": "^3.3.6",
     "vite": "^5.2.11"