Add setting to allow different URL for front-end and back-end for correct sitemap

For all our websites we use different URL for front-end and back-end.
In our case it's "www.example.com" for website visitors (front-end) and "intern.example.com" for the backend.

This is for various reasons, mainly security (www.example.com prevents accessing the /administrator path) and intern.example.com is heavily secured.
Also for caching reasons where www.example.com runs over a CDN and intern.example.com is direct webserver access limited to our own IPs.

There is a setting in Joomla in configuration.php for this called $live_site so it would be called "$live_site = 'https://www.example.com'".
When this option is set RSSeo! uses that setting and even when accessing the backend using "https://intern.example.com/administrator" RSSeo! will create correct URLs in the sitemap using www.example.com.

Example for "/contact" ($live_site = ''):
Accessing RSSeo! via backend "https://intern.example.com/administrator"
Sitemap would generate: "https://intern.example.com/contact" (not good! that's the backend URL and it needs to be corrected manually afterwards)

Example for "/contact" ($live_site = 'https://www.example.com'):
Accessing RSSeo! via backend "https://intern.example.com/administrator"
Sitemap would generate: "https://www.example.com/contact" (correct)

Unfortunately Joomla's configuration field "$live_site" is causing all sorts of issues within Joomla and basically everyone tells you "dont't use it, it's as old as Joomla 1.x". So I stopped using it because of the issues it causes and now, whenever I create a sitemap in RSSeo! I manually edit the file afterwards and replace all "intern" by "www".

The feature request is to add a configuration field where the live URL can be entered and RSSeo! will use that to create correct sitemaps instead of (or in addition) to the $live_site configuration option.
The basic functionality for this is already implemented in RSSeo! (it's reacting correctly to the $live_site config).