Allow setting max_age on static files via config

Uses the SEND_FILE_MAX_AGE_DEFAULT config var for compatibility with
Flask's default static file server.

ai_web_common/flask_ai/app.py

@@ -37,6 +37,8 @@ def init_app(app, talisman):
         root=pkg_resources.resource_filename(
             app.import_name, 'static'),
         prefix='static/',
+        max_age=app.config.get(
+            'SEND_FILE_MAX_AGE_DEFAULT', 86400*365),
     )
 
     if 'SUPPORTED_LANGUAGES' not in app.config: