Retry requests / aiohttp-level errors

[cocoon333]

Calling user on async client causes these two errors sometimes:

Code for calling get_user:

Errors often result in unclosed client sessions

[tybug]

please post the full stacktrace for both errors

[cocoon333]

full stack trace:

[tybug]

Tempted to say this is "not our problem" in the absence of a reliable repro case, given the message implies this is osu-web side.

Likely the best we can do here is provide an automatic retry mechanism for network errors.