node join support

[danthegoodman1]

The issue is that node join support is not super elegant https://pkg.go.dev/github.com/lni/dragonboat/v4#NodeHost.StartReplica

• starting a brand new Raft shard, set join to false and specify all initial member node details in the initialMembers map.
• joining a new node to an existing Raft shard, set join to true and leave the initialMembers map empty. This requires the joining node to have already been added as a member node of the Raft shard.
• restarting a crashed or stopped node, set join to false and leave the initialMembers map to be empty. This applies to both initial member nodes and those joined later.

This means we have to know between an initial join, and a restart. We also need to know if it's an initial member or not. It seems that the initial member is not damaging when recovering: https://github.com/lni/dragonboat-example/blob/master/helloworld/main.go#L128C2-L132C25

// when joining a new node which is not an initial members, the initialMembers // map should be empty. // when restarting a node that is not a member of the initial nodes, you can // leave the initialMembers to be empty. we still populate the initialMembers // here for simplicity.

The reason is that dragonboat "recruits" members my reaching out to them and telling them to join, so they need to understand that they are in the join phase. In order to handle joining, it would be nice if we can detect that this is not an initial member, and if there's local state of already being in a cluster.

[danthegoodman1]

What we need to do is override the initialMembers to nothing if join is provided, and non-initial nodes should always leave join provided

[danthegoodman1]

Or even better, we just detect whether it's an initial node or not based on it's URL and the initialMembers

[danthegoodman1]

Initial cluster will bootstrap with shard 0

[danthegoodman1]

kinds of depends on shard creation, but mostly done