Clarify existing app behavior when being upgraded [ci skip]
Clarify existing app behavior when being upgraded [ci skip]

Closes #39213.

BlakeWilliams/rails,georgeclaghorn/rails,Edouard-chin/rails,Stellenticket/rails,schuetzm/rails,georgeclaghorn/rails,rafaelfranca/omg-rails,tjschuck/rails,lcreid/rails,bogdanvlviv/rails,Stellenticket/rails,schuetzm/rails,Envek/rails,bogdanvlviv/rails,yahonda/rails,tgxworld/rails,betesh/rails,Edouard-chin/rails,repinel/rails,Vasfed/rails,Envek/rails,Vasfed/rails,tgxworld/rails,repinel/rails,rails/rails,lcreid/rails,kmcphillips/rails,MSP-Greg/rails,betesh/rails,kddeisz/rails,Erol/rails,Vasfed/rails,schuetzm/rails,tgxworld/rails,joonyou/rails,BlakeWilliams/rails,kddeisz/rails,rails/rails,kmcphillips/rails,eileencodes/rails,Erol/rails,starknx/rails,esparta/rails,MSP-Greg/rails,tjschuck/rails,georgeclaghorn/rails,Erol/rails,tjschuck/rails,BlakeWilliams/rails,Vasfed/rails,joonyou/rails,schuetzm/rails,vipulnsward/rails,kddeisz/rails,rails/rails,yahonda/rails,joonyou/rails,starknx/rails,repinel/rails,eileencodes/rails,MSP-Greg/rails,betesh/rails,betesh/rails,vipulnsward/rails,georgeclaghorn/rails,Stellenticket/rails,vipulnsward/rails,esparta/rails,kmcphillips/rails,yawboakye/rails,joonyou/rails,yawboakye/rails,starknx/rails,lcreid/rails,kmcphillips/rails,yawboakye/rails,lcreid/rails,esparta/rails,Stellenticket/rails,rafaelfranca/omg-rails,EmmaB/rails-1,bogdanvlviv/rails,Edouard-chin/rails,repinel/rails,rafaelfranca/omg-rails,esparta/rails,vipulnsward/rails,Envek/rails,tjschuck/rails,yalab/rails,MSP-Greg/rails,eileencodes/rails,Envek/rails,kddeisz/rails,bogdanvlviv/rails,eileencodes/rails,BlakeWilliams/rails,yalab/rails,yalab/rails,yalab/rails,yahonda/rails,Edouard-chin/rails,yahonda/rails,Erol/rails,tgxworld/rails,EmmaB/rails-1,yawboakye/rails,rails/rails,EmmaB/rails-1