Allow timeout on v2 Client requests

[DashKenny]

Hi,

I've been looking into some long running requests we've got, and noticed that the reason appears to be that Tweepy does not set (or allow you to set) a timeout on BaseClient.request in any way. This means that when doing simple things such as trying to get a user, we are waiting for 15 minutes.

It would be great to have more control of the retries on the client and not get stuck for so long. I could make a PR to easily allow setting a global timeout on the client. Additionally we could update the existing methods to take in an override timeout as well if we wanted.