Store logical topology as a single KV entry instead of N entries

Currently, logical topology (which is a set of consistent IDs of the nodes that joined the cluster) is stored like this: if we have N nodes in the logical topology, we store N entries, one per node.

IGNITE-18085 requires us to handle logical topology as a whole, also we need to store the logical topology version (incrementing it on each change). So we should store a BLOB representing the node names and topology version under a single key.