allow unix-socket connection in RedisSettings (socket_address)

[lazToum]

following the recommendation in #209 (comment)

[samuelcolvin]

I'm wondering how this will interact with #259? I want to get that merged before the next release.

[lazToum]

It will probably need a few minor modifications. (adding a unix_socket_path init argument according to https://github.com/aio-libs/aioredis-py/blob/56d6b325ee246a3eb0fc8bb6803247c86bb2f494/aioredis/client.py#L845
Of course, I can work on it again later, after #259 is merged.

[samuelcolvin]

#259 is merged, if you still want to work on this, I'd be happy to review an update.

[lazToum]

Nice!
currently waiting for redis/redis-py#2046 (for UnixDomainSocketConnection) and yahoo/redislite#153 (for redislite/testing on python 3.10)

[lazToum]

I think it's ready, as long as we have redis>=4.2.0rc3.
The actual changes (apart from the tests) are these:
https://github.com/lazToum/arq/blob/master/arq/connections.py#L42-L71
and
https://github.com/lazToum/arq/blob/master/arq/connections.py#L226-L233
Should I close this PR and start a new one on the updated master branch?

[samuelcolvin]

There's lots of conflicts here, you'll need to rebase/merge with master.