upstream: allow active health check to set degraded (#5374)

This allows a host to be marked as degraded by having x-envoy-degraded
returned from the HTTP active health checking response.

Signed-off-by: Snow Pettersen <snowp@squareup.com>

Mirrored from https://github.com/envoyproxy/envoy @ 7b6d7a2706ac5290e5e87535c23c11def49275db

envoy/admin/v2alpha/clusters.proto

@@ -71,6 +71,9 @@ message HostHealthStatus {
   // The host is currently considered an outlier and has been ejected.
   bool failed_outlier_check = 2;
 
+  // The host is currently being marked as degraded through active health checking.
+  bool failed_active_degraded_check = 4;
+
   // Health status as reported by EDS. Note: only HEALTHY and UNHEALTHY are currently supported
   // here.
   // TODO(mrice32): pipe through remaining EDS health status possibilities.