add config and init for server timings (#1368)

* add config and init for server timings

* add missing config error check

server/app/app.py

@@ -4,6 +4,7 @@ import logging
 from flask import Flask, redirect, current_app, make_response, render_template, abort
 from flask import Blueprint, request
 from flask_restful import Api, Resource
+from server_timing import Timing as ServerTiming
 
 from http import HTTPStatus
 
@@ -235,6 +236,8 @@ class Server:
         self.app = Flask(__name__, static_folder="../common/web/static")
         self._before_adding_routes(app_config)
         self.app.json_encoder = Float32JSONEncoder
+        if app_config.server__server_timing_headers:
+            ServerTiming(self.app, force_debug=True)
 
         # enable session data
         self.app.permanent_session_lifetime = datetime.timedelta(days=50 * 365)