health_check: add header matching to health check http filter (#3129)

Implements the header matching mechanism that was added to the API in #3097 .

Risk Level: Low

Testing: Unit tests were added for the new configuration options.

Docs Changes: #3097.

Release Notes: added release note.

Signed-off-by: Matt Rice <mattrice@google.com>

Mirrored from https://github.com/envoyproxy/envoy @ 132b36cdae221dd602ebd920a1025167c3a7753a

envoy/config/filter/http/health_check/v2/health_check.proto

@@ -32,7 +32,6 @@ message HealthCheck {
   // must be healthy in order for the filter to return a 200.
   map<string, envoy.type.Percent> cluster_min_healthy_percentages = 4;
 
-  // [#not-implemented-hide:]
   // Specifies a set of health check request headers to match on. The health check filter will
   // check a request’s headers against all the specified headers. To specify the health check
   // endpoint, set the ``:path`` header to match on. Note that if the