fix(metrics): normalize peer-health key so servers_offline_total counts each peer once
rustfs_cluster_servers_offline_total is the count of distinct keys in the
addr-keyed CLUSTER_PEER_HEALTH map. The data path keys a peer by
endpoint.grid_host() (scheme://host:port) while the lock path keys it by
url::Url::to_string() (scheme://host:port/, trailing slash), so one physical
peer becomes two health entries and a single downed node reports 2 (2N for N).
Normalize the address (trim trailing slashes) at the map boundary in
record_peer_reachable/record_peer_unreachable/cluster_peer_is_offline/
cluster_peer_should_bypass so both forms collapse to one canonical key.
Pure observability fix; peer selection and quorum are unchanged.
Fixesrustfs/backlog#1043
Co-authored-by: heihutu <[email protected]>
