With alpha2 without using the constraints https://github.com/apache/airflow/blob/constraints-master/constraints-3.6.txt , when accessing Webserver it fails with

```
Something bad has happened.
Please consider letting us know by creating a bug report using GitHub.

Python version: 3.6.12
Airflow version: 2.0.0a2
Node: 599861bd62ac
-------------------------------------------------------------------------------
Traceback (most recent call last):
  File "/usr/local/lib/python3.6/site-packages/flask/app.py", line 2447, in wsgi_app
    response = self.full_dispatch_request()
  File "/usr/local/lib/python3.6/site-packages/flask/app.py", line 1953, in full_dispatch_request
    return self.finalize_request(rv)
  File "/usr/local/lib/python3.6/site-packages/flask/app.py", line 1970, in finalize_request
    response = self.process_response(response)
  File "/usr/local/lib/python3.6/site-packages/flask/app.py", line 2269, in process_response
    self.session_interface.save_session(self, ctx.session, response)
  File "/usr/local/lib/python3.6/site-packages/flask/sessions.py", line 387, in save_session
    samesite=samesite,
  File "/usr/local/lib/python3.6/site-packages/werkzeug/wrappers/base_response.py", line 479, in set_cookie
    samesite=samesite,
  File "/usr/local/lib/python3.6/site-packages/werkzeug/http.py", line 1217, in dump_cookie
    raise ValueError("SameSite must be 'Strict', 'Lax', or 'None'.")
ValueError: SameSite must be 'Strict', 'Lax', or 'None'.
```
setup.py
'apache.beam': apache_beam,
    "apache.cassandra": cassandra,
    "apache.druid": druid,
    "apache.hdfs": hdfs,
    "apache.hive": hive,
    "apache.kylin": kylin,
    "apache.pinot": pinot,
    "apache.webhdfs": webhdfs,
    'async': async_packages,
    'atlas': atlas,  
    'aws': amazon,  
    'azure': azure,  
    'cassandra': cassandra,  
    'celery': celery,
    'cgroups': cgroups,
    'cloudant': cloudant,
    'cncf.kubernetes': kubernetes,
    'dask': dask,
    'databricks': databricks,
    'datadog': datadog,
    'devel': devel_minreq,
    'devel_hadoop': devel_hadoop,
    'doc': doc,
    'docker': docker,
    'druid': druid,  
    'elasticsearch': elasticsearch,
    'exasol': exasol,
    'facebook': facebook,
    'gcp': google,  
    'gcp_api': google,