[TASK] Abandon and archive this repo/extension

[dkd-kaehm]

What should be done in the scope of this task?

EXT:solrfluidgrouping is a part of EXT:solr 12.0.0+, so only the TYPO3 >=9.5 <=11.5 are maintained now.

• [TASK] A hint about "abandoned due merge in EXT:solr" in each 10 - 11.0.x release commit #35
• Add a hint to readme
• Add it to replaces on EXT:solr https://github.com/TYPO3-Solr/ext-solr/blob/a528113bf7a0861c8ec6632c4db89e3eb43f8889/composer.json#L49-L53
• etc.