feat: generic datatype for node ID

[vidarandrebo]

The node id is now a unint32, but this does not always match up with the applications utilizing gorums. If an application does not use a uint32, it would either have to resolve a node from the config using ip address, or store and exchange gorums ids at the application level.

[meling]

I think it makes sense to implement a generic node ID or a mapping from IP to a generic node ID, to avoid having separate Gorums IDs and application-level IDs. However, it would be nice to do a deeper analysis of Gorums' codebase to examine if this could cause problems in some way. @hanish520 @johningve @leandernikolaus Do you foresee any issues with this? (I haven't had time to dig into it myself yet.)