Support for auto-failover of Index Service - Cluster Mgmt

It is currently possible to enable automatic failover of nodes running the Index service by toggling an internal setting. Given the improvements we are introducing with Replica Indexes and Rebalancing, should we allow this by default in a future release, without the need to use an internal setting?

The current logic will allow the failover of an Index node as long as there are two nodes running the service.

When customers are using Equivalent Indexes, we generally advise them to have multiple copies of Indexes for HA purposes - should we explicitly check that we are not removing the last instance of an Index before failing over the node?

If customers are using Replica Indexes, will we automatically instantiate a new replica copy at failover time?

Is there any difference in behaviour between Adhoc and Prepared Queries when an Index node is failed over?

We have a quota on the number of nodes that can be automatically failed over without some kind of intervention (currently one). Does this quota need to be extended to track/limit the number of nodes with different services on that have been failed over? Any reason why we can't failover (for example) one Data node and one Index node at the same time?

MB-12740 suggests that we should allow failing over as many nodes as we have bucket replicas - does the same logic apply to the number of Index Replicas?

PRD - https://docs.google.com/document/d/1QbQ3rWPPUHRsHj_Yf_0x7gYhrsP5KQSgDRl5jZy4_Wo/edit