SQLAlchemy engine configuration is not passed to FAB based UI. Faced this issue when running Airflow with MySQL metadata store with wait_timeout = 120. Webserver is failing with Internal Server Error due to "[MySQL Server has gone away](https://docs.sqlalchemy.org/en/13/faq/connections.html#mysql-server-has-gone-away)" error. Settings like `sql_alchemy_pool_recycle` and  `sql_alchemy_pool_pre_ping` have no impact on FAB internal communication with MySQL.

**Apache Airflow version**: 1.10.12
tests/www/test_app.py
#
#
#
import unittest
from unittest import mock
from werkzeug.routing import Rule
from werkzeug.test import create_environ
from werkzeug.wrappers import Response
from airflow.www import app as application
from tests.test_utils.config import conf_vars
class TestApp(unittest.TestCase):
    @classmethod
    def setUpClass(cls) -> None:
        from airflow import settings
        settings.configure_orm()
    @conf_vars({
        ('webserver', 'enable_proxy_fix'): 'True',
        ('webserver', 'proxy_fix_x_for'): '1',
        ('webserver', 'proxy_fix_x_proto'): '1',
        ('webserver', 'proxy_fix_x_host'): '1',
        ('webserver', 'proxy_fix_x_port'): '1',
        ('webserver', 'proxy_fix_x_prefix'): '1'
    })
    @mock.patch("airflow.www.app.app", None)
    def test_should_respect_proxy_fix(self):