Allow the module to work without Domain Access (using only the available domain source option)

Problem/Motivation

We have a site which uses domain module and domain source, also domain contexts. We use domain source to redirect to correct domain on content when needed, and otherwise allow access to the content from each domain. Leaving domain_access disabled for the scale of the site has simplified our domain setup significantly and enabling it breaks a lot of access on the site.

We would love to see a working release that does not need the domain_access module.

Steps to reproduce

We tried taking out the dependency as suggested in this ticket with no luck: https://www.drupal.org/project/domain_simple_sitemap/issues/2981616 ✨ Can you make it not require "Domain Access" ? Closed: outdated

We get this in our logs when attempting to generate a sitemap:

Error: Class "Drupal\domain_access\DomainAccessManagerInterface" not found in Drupal\domain_simple_sitemap\Plugin\simple_sitemap\UrlGenerator\DomainEntityUrlGenerator->getDataSets() (line 80 of /var/www/html/docroot/modules/contrib/domain_simple_sitemap/src/Plugin/simple_sitemap/UrlGenerator/DomainEntityUrlGenerator.php).

Proposed resolution

Make domain_access module optional (require domain but not domain_access) and continue to allow users to pick between generating the site-map with either domain_access or domain_source, as was made possible here: https://www.drupal.org/project/domain_simple_sitemap/issues/3462430 🐛 Index only content checked as Domain source Needs review

I don't know exactly whats needed to make this work as I'm largely unfamiliar with the code, but with some advice on where to start I'd be happy to take it on and supply a patch.