chore: Update admin build/serve configuration (#9584)

**Breaking changes**

The `outDir` has been deprecated and wont be used anymore, instead all the path are computed internally following these rules
- if admin is not `disabled` and the `build` command is run without the `--admin-only` flag, then the admin output dir will be `.medusa/server/public/admin` and it will be served from that same location from the medusa instance.
- if admin is not `disabled` and the `build` command is run with the `--admin-only` flag, then the admin output dir will be `.medusa/admin` with the purpose of deploying the admin separately. ⚠️ (expect to receive a warning log)
- if the admin is `disabled` and the `build` command is run with the `--admin-only` flag, then fallback to rule number 2

| admin enabled  | medusa build --admin-only  | output dir |
|---|---|---|
| true  | true  | `.medusa/admin` ⚠️ (expect to receive a warning log) |
| true  | false  | `.medusa/server/public/admin`  |
| false  | true  | `.medusa/admin`  |
| false  | false  | none |

```diff
// medusa-config.ts

{
  // ...
  admin: {
-    outDir: 'some/path'
  }
}
```


cc @kasperkristensen @sradevski @olivermrbl

packages/admin/admin-bundler/src/types.ts

@@ -1,6 +1,7 @@
 import { AdminOptions } from "@medusajs/types"
 
-export type BundlerOptions = Required<Pick<AdminOptions, "outDir" | "path">> &
+export type BundlerOptions = Required<Pick<AdminOptions, "path">> &
   Pick<AdminOptions, "vite" | "backendUrl" | "storefrontUrl"> & {
+    outDir: string
     sources?: string[]
   }