Rename confusing endpoints

[masnax]

In particular, /cluster/1.0/cluster is a bit stammering, so we can rename it to /cluster/1.0/members instead.

/cluster is the start point for built-in microcluster API endpoints /cluster/1.0 is the start point for all publicly accessible microcluster API endpoints (issuing tokens, listing cluster members, etc.). /cluster/1.0/cluster is the subset of those endpoints that manages cluster formation.

In particular, these endpoints are

POST /cluster/1.0/cluster -- adds a cluster member to dqlite GET /cluster/1.0/cluster -- lists existing cluster member information DELETE /cluster/1.0/cluster/{name} -- deletes the cluster member with the given name.

Since all of these pertain to cluster members, we can simply rename the endpoint to /cluster/1.0/members to be a bit less confusing.

This would be an API change and should happen with a new API extension.