Clarify Solr version compatibility

[rachelwhitton]

Re: Pantheon Search (formerly Pantheon Solr)

Priority: Medium

Issue Description:

Reported by @matthewboman
Seeing some customer confusion on our Solr docs https://docs.pantheon.io/solr

Specifically this section

Pantheon Search supports Search API Solr 8.x-1.x, which is currently unsupported by Solr. Search API Solr 8.x-1.x should continue to work as long as the Search API Pantheon module is also being used, following the installation directions below.

• what does "currently unsupported by Solr" mean?
• the link to https://www.drupal.org/project/search_api_solr does not have 8.x-1.x. It has 4.3/4.2. Do we mean Search API https://www.drupal.org/project/search_api ? or Search API Pantheon https://www.drupal.org/project/search_api_pantheon?

[rachelwhitton]

Reported by @kporras07

Also the docs sometimes when talk about Solr, really refer to Solr3 and treat Solr8 as a separate thing in totally different pages

[cleverington]

Might toss a ping that this documentation page is still heavily outdated and needs a lot of cleanup to be something usable for selling Solr to Agencies clients (instead of being used as a reason to not use Pantheon when Clients would like to).

https://docs.pantheon.io/solr

Just this line alone, when Solr 9 is out and Solr 8 has releases up to 8.11.3 is very awkward:

Currently, Pantheon provides Apache Solr v3.6 and v8.0 as a service for all plans except the Basic plan.