Upgrade aiohttp to 3.9 series

[achimnol]

Let's upgrade aiohttp to the 3.9 series.

• Update the unified requirements.txt and regenerate the lockfiles by pants generate-lockfiles --resolve=python-default #1795
• Adopt AppKey to remove manual type annotations when accessing RootContext and PrivateContext in ai.backend.manager.api sub-apps.
  • ref) https://docs.aiohttp.org/en/stable/web_advanced.html#application-s-config

[achimnol]

Done in #1855.