Eliminate race on topology entry in metakv on GetNodeInfo() updates

When an analytics node is providing node info to ns_server, it will update any changes in the stored topology in metakv. This is unsafe, as this could cause us to lose a topology update written by the coordinator. This should be reworked such that the topology entry in metakv is only ever written by the coordinator.

If this can be done in such a way that is mixed-mode friendly, this should be taken in 7.2.5 & 7.6.1.
EDIT: due to how we allocate node priorities including based on patch version, this can safely be done in patch releases (e.g. 7.2.5).