Add runner management health check for /ping

Even though we can check the health of the runner management, we would like to ensure an external health check validates the availability of all required services.

app/controllers/ping_controller.rb

@@ -1,7 +1,7 @@
 # frozen_string_literal: true
 
 class PingController < ApplicationController
-  before_action :postgres_connected!
+  before_action :postgres_connected!, :runner_manager_healthy!
   after_action :verify_authorized, except: %i[index]
 
   def index
@@ -20,4 +20,11 @@ class PingController < ApplicationController
 
     raise ActiveRecord::ConnectionNotEstablished
   end
+
+  def runner_manager_healthy!
+    # any unhandled exception leads to a HTTP 500 response.
+    return if Runner.strategy_class.health == true
+
+    raise Runner::Error::InternalServerError
+  end
 end