Failed to create 'themes' or 'plugins' directories if the `--skip-content` flag is used.

The following command is used to create a new site.

```
ee site create example.com --type=wp --title=XX --admin-user=xxx --skip-content --ssl=le
```
Attention to `--skip-content` flag.

After the installation is done, WP works great.

But if I try to install a theme or a plugin, it will fail, because can't create the respective directories.

```
Installation failed: Could not create directory.
```

This issue has been there for years, and I always created these dirs manually and set the needed permissions. But would be great the have them created automatically.

The `uploads` folder does not have this problem. It's created automatically on the first file upload.

System Information
- On any EE v4. This issue has been there in all Ubuntu dist that I've used: 16.04 --- 20.04