Make `allowDomain` in WordPress to be configurable

### What feature is it?

Make [`allowDomain`](https://github.com/DIYgod/RSSHub/blob/master/lib/routes/blogs/wordpress.js#L3) configurable via environment variables.

### What problem does this feature solve?

Currently, the [`allowDomain`](https://github.com/DIYgod/RSSHub/blob/master/lib/routes/blogs/wordpress.js#L3) can only be changed by modifying the source code. The is not good if you deployed using Docker.

### Additional description

_No response_

### This is not a duplicated feature request or new RSS proposal

- [X] I have searched [existing issues](https://github.com/DIYgod/RSSHub/issues) to ensure this feature has not already been requested and this is not a [new RSS proposal](https://github.com/DIYgod/RSSHub/issues/new?assignees=&labels=RSS+proposal&template=rss_request_en.yml).