[leo_storage] Allow users to choose a network for each (online/offline) processing

[mocchira]

In order to avoid the offline processing affecting the online processing in terms of network bandwidth. This feature will be important when someone try to build LeoFS as a service and guarantee its users with SLA including a minimum bandwidth and a maximum latency etc even while some maintenance is going on.

Notes:

• What the online processing is
  • GET/PUT/DELETE/HEAD/LISTING requests from gateway nodes
  • Subsequent read_repair and replicate requests from storage nodes
• What the offline processing is
  • Recover (object|disk|node|cluster) requests from storage/manager nodes
  • Delete (bucket|directory) requests from storage/manager nodes
  • Rebalance requests from manager nodes

[mocchira]

Reference IMPL

• https://docs.openstack.org/swift/latest/replication_network.html