raft: Remove NodeID config

In the previous integration attempt, Raft used a static node ID as a
unique identifier. That approach was deemed ineffective. Gitaly uses
"storage" as an encapsulated functional unit. A server might serve
requests targeting multiple storage at the same time. Adding another ID
system increases the complexity and might conflict with the existing
storage system. In addition, in scenarios like a node joins/re-joins,
re-using a static node ID might need extra handling to avoid conflicts.

As a result, Raft will use an automatic node ID system based on node
joining events instead. This commit removes obsolete NodeID config.