Revamp peer recovery flow for remote backed indexes

[sachinpkale]

• Currently, peer recovery for remote backed indexes works in 2 modes.

• Target node downloads latest segments from remote segment store and the incremental segments (that are created on source while target was downloading the segments) are copied node-to-node from source to target.

• This bi-modal behavior may create confusion or even regression if we build a feature that assumes no data copy between the two nodes.

• In this feature request, we want to restrict data source at one place for remote backed indexes: remote segment store

• More details to be added

[ashking94]

for remote store, it should not be called peer recovery any more, but may be something else like "Remote store recovery".