mgr/orchestrator: add filtering and count option for orch host ls

mgr/orchestrator: add filtering and count option for orch host ls

Filter orch host ls output for only hosts whose name
contains a certain substring or who have a certain label

Add a count flag that causes the command to return the number
of hosts found (either overall or matching the substring and/or
label) instead of a list of all the matching hosts

Fixes: https://tracker.ceph.com/issues/47774
Fixes: https://tracker.ceph.com/issues/53452
Signed-off-by: Adam King <adking@redhat.com>