This change replaces the `httpx` client with `aiohttp` for the
RetroAchievements API service.
The main reason for this change is that `httpx` has an unavoidable log
line with `INFO` level, which includes the request full URL, containing
the user's API key.
`httpx` has had an
[open discussion](https://github.com/encode/httpx/discussions/2765)
regarding this security issue for almost two years.
The change to `aiohttp` is painless, and would allow us to migrate more
of the codebase to it in the future, to avoid leaking sensitive
information in logs.
