[Meta] Solr 9 Support

Adding the Solr 9 → tag and updating Issue Summary.

Among the 50,700 sites reporting using the module, there are probably big companies, organizations, and Solr hosting service providers. It would be really awesome if one or more of them would consider sponsoring creating a Solr 9 supporting version.

This is Open Source after all, and the free software we all enjoy, doesn't write itself :-)

@mkalkbrenner: It might help decision makers evaluate if they want to sponsor Solr 9 support if you shared how long you estimate it would take, and what the budget is, under the "Funding" header?

Adding PR on Github.

Adding tag.

Automatically closed - issue fixed for 2 weeks with no activity.