feat: add HEAD method for health check APIs (#802)

The HEAD method is in addition to the GET method
for liveness and readiness APIs

Fixes #796

Author: nikhilsinhaparseable

server/src/handlers/http/modal/server.rs

@@ -368,14 +368,20 @@ impl Server {
 
     // get the live check
     // GET "/liveness" ==> Liveness check as per https://kubernetes.io/docs/tasks/configure-pod-container/configure-liveness-readiness-startup-probes/#define-a-liveness-command
+    // HEAD "/liveness"
     pub fn get_liveness_factory() -> Resource {
-        web::resource("/liveness").route(web::get().to(health_check::liveness))
+        web::resource("/liveness")
+            .route(web::get().to(health_check::liveness))
+            .route(web::head().to(health_check::liveness))
     }
 
     // get the readiness check
     // GET "/readiness" ==> Readiness check as per https://kubernetes.io/docs/tasks/configure-pod-container/configure-liveness-readiness-startup-probes/#define-readiness-probes
+    // HEAD "/readiness"
     pub fn get_readiness_factory() -> Resource {
-        web::resource("/readiness").route(web::get().to(health_check::readiness))
+        web::resource("/readiness")
+            .route(web::get().to(health_check::readiness))
+            .route(web::head().to(health_check::readiness))
     }
 
     // get the about factory