add config and init for server timings (#1368)

* add config and init for server timings

* add missing config error check

server/common/app_config.py

@@ -67,6 +67,7 @@ class AppConfig(object):
             self.server__force_https = dc["server"]["force_https"]
             self.server__flask_secret_key = dc["server"]["flask_secret_key"]
             self.server__generate_cache_control_headers = dc["server"]["generate_cache_control_headers"]
+            self.server__server_timing_headers = dc["server"]["server_timing_headers"]
 
             self.multi_dataset__dataroot = dc["multi_dataset"]["dataroot"]
             self.multi_dataset__index = dc["multi_dataset"]["index"]
@@ -201,6 +202,7 @@ class AppConfig(object):
         self.__check_attr("server__force_https", bool)
         self.__check_attr("server__flask_secret_key", (type(None), str))
         self.__check_attr("server__generate_cache_control_headers", bool)
+        self.__check_attr("server__server_timing_headers", bool)
 
         if self.server__port:
             if not is_port_available(self.server__host, self.server__port):

server/common/default_config.py

@@ -15,6 +15,7 @@ server:
   force_https: false
   flask_secret_key: null
   generate_cache_control_headers: false
+  server_timing_headers: false
 
 presentation:
   max_categories: 1000