Allow specifying / overriding the prefix / suffix per entity

Thinking about this a bit more, I think we should implement this as a Metatag extending module to use it's well known functionality and ecosystem. See ✨ Submodule to override the (visible) page title ("metatag_page_title") Active

Then we could deprecate this module in favor of that and might not only solve this, but also have features like cross-entity-support out of the box.

Finally there's an initial implementation for such a module now: https://www.drupal.org/project/metatag_page_heading →

But I'll leave this open for the future due to the different approaches.