Add .PutKVPairs() method to KVStore interface

[timvaillancourt]

Related issue: #1273

Description

This PR adds the .PutKVPairs() function to the KVStore interface (from go/kv/kv.go) to allow decisions around updating multiple KVs to be pushed down to the various KV store implementations. This new method replaces the single-KVPair method .PutKVPair() from go/kv/kv.go

The following files were updated to use .PutKVPairs() vs single-KVPair updates:

1. go/logic/command_applier.go
2. go/logic/orchestrator.go
3. go/logic/topology_recovery.go

For now the .PutKVPairs() function in each KVStore is just doing a plain-loop over .PutKeyValue(). In the near-future this method will be used to implement atomic multi-KVPair updates for the Consul KV store (#1273) and potentially the Internal/ZooKeeper store, too

cc @shlomi-noach

[shlomi-noach]

The addition of PutKVPairs() is good and makes sense. See inline a comment on how PutKVPairs() is used within orchestrator.go

[timvaillancourt]

Updated PR based on @shlomi-noach's suggestions

[shlomi-noach]

Looks good with minor suggested change.