[1/3] Start a rexi_server per remote node

This is part of a multi-release upgrade to switch to using a rexi_server
instance per remote node. The first commit introduces the new
rexi_server instances, the second switches to using the new instances
and the third will remove the singleton rexi_server. Each of these
commits should be in a separate release.

The new pattern introduced by this commit will start a 'rexi_server_%b'
process where the '%b' is replaced by the `erlang:phash2(Node)` for
which it will service requests. After the second commit is release each
rexi generated message will be sent to the rexi_server instance on the
remote node handling requests for the local node. The
`rexi_utils:server_pid/1` function is used to generate the id of the
remote server.
Merge '[1/3] Start a rexi_server per remote node'

BugzID: 18215