Update search code to use zoekt_enabled_namespace.replicas.ready.last
Currently, we are checking if the index is ready. After incorporating the chunking strategy, we should check the replicas instead.
Code to be change should be here: https://gitlab.com/gitlab-org/gitlab/-/blob/ed93b1599080248828032d10183b73cdbe45c87b/ee/app/models/search/zoekt.rb#L21
Edited by Ravi Kumar