Add ProxyPreserveHost directive to apache config

docker/apache-config

@@ -28,6 +28,7 @@ ServerName ${DJANGO_PRIMARY_FQDN}
   # Aliases for docs and admin_docs
   Alias /documentation/ "/home/gracedb/gracedb_project/docs/user_docs/build/"
   Alias /admin_docs/ "/home/gracedb/gracedb_project/docs/admin_docs/build/"
+  ProxyPreserveHost on
   ProxyPass "/robots.txt" "!"
   ProxyPass "/shibboleth-ds" "!"
   ProxyPass "/Shibboleth.sso" "!"