[FEATURE] Add an event to be able to modify the domain used for a site

[pschriner]

Is your feature request related to a problem? Please describe.
When running the TYPO§ backend on a different domain than the TYPO3 frontend it is impossible to influence the frontend index from the TYPO3 backend.

Describe the solution you'd like
I'd like to have a PSR-14 event to modify the domain used by solr.

Describe alternatives you've considered
I'm currently using a composer patch, but I'd rather not use one.

Additional context
For context: I need it here https://gitlab.opencode.de/bmi/government-site-builder-11/extensions/gsb_solr

Target versions
main, 12