More flexible CCS version compatibility between clusters

Customers with multiple clusters connected together via CCS struggle with planning stack upgrades The current version compatibility model requires customers to upgrade the local cluster last. As a result, the central/local cluster might end up remaining on an older, potentially vulnerable version of the stack because remotes are not upgraded yet.

Customers solve this today by maintaining a dedicated cluster for cross-cluster search. Keeping this cluster on the earliest version needed to search the other clusters. For example, if you have 7.17 and 8.x clusters, you can maintain a dedicated 7.17 cluster to use as the local cluster for cross-cluster search. Or they keep each cluster no more than one minor version apart. This lets them use any cluster as the local cluster when running a cross-cluster search.

We would like to allow remote versions to diverge by more than v-1