admin: add host priority to cluster response (#7317)

Add host priority to cluster response in admin server.

Risk Level: low
Testing: unit test
Docs Changes: N/A
Release Notes: updated

Signed-off-by: Yan Xue <yxyan@google.com>

Mirrored from https://github.com/envoyproxy/envoy @ 815c506c96ef441d99341775af2125d58d644b8f

envoy/admin/v2alpha/clusters.proto

@@ -68,6 +68,9 @@ message HostStatus {
 
   // The hostname of the host, if applicable.
   string hostname = 6;
+
+  // The host's priority. If not configured, the value defaults to 0 (highest priority).
+  uint32 priority = 7;
 }
 
 // Health status for a host.