Fix documentation for joins across clusters
Fix documentation for joins across clusters

We weren't able to get our gem for splitting across clusters into Rails
for 6.1. We're hoping to have that work completed for 7.0 but I should
have never promised in the docs to get it done by a specific time.

Ref #41537

BlakeWilliams/rails,kmcphillips/rails,yawboakye/rails,betesh/rails,kmcphillips/rails,yahonda/rails,kmcphillips/rails,Stellenticket/rails,Vasfed/rails,kddeisz/rails,Stellenticket/rails,kmcphillips/rails,esparta/rails,georgeclaghorn/rails,lcreid/rails,joonyou/rails,rails/rails,Stellenticket/rails,Envek/rails,BlakeWilliams/rails,joonyou/rails,georgeclaghorn/rails,MSP-Greg/rails,kddeisz/rails,lcreid/rails,Envek/rails,georgeclaghorn/rails,Edouard-chin/rails,betesh/rails,rails/rails,Edouard-chin/rails,MSP-Greg/rails,Stellenticket/rails,yawboakye/rails,bogdanvlviv/rails,Envek/rails,Edouard-chin/rails,Vasfed/rails,lcreid/rails,lcreid/rails,Erol/rails,Erol/rails,Vasfed/rails,yawboakye/rails,EmmaB/rails-1,bogdanvlviv/rails,kddeisz/rails,Erol/rails,joonyou/rails,rails/rails,esparta/rails,bogdanvlviv/rails,MSP-Greg/rails,joonyou/rails,MSP-Greg/rails,EmmaB/rails-1,Erol/rails,BlakeWilliams/rails,yawboakye/rails,EmmaB/rails-1,betesh/rails,rails/rails,kddeisz/rails,betesh/rails,esparta/rails,BlakeWilliams/rails,bogdanvlviv/rails,georgeclaghorn/rails,Envek/rails,yahonda/rails,Edouard-chin/rails,esparta/rails,yahonda/rails,Vasfed/rails,yahonda/rails