Add more info to UnexpectedStatus exception

[M1troll]

Problem

Now when we set

raise_on_unexpected_status=True

in the client, we will only see Unexpected status code: 400 (or smt like) when any unexpected status is received. But in fact, this is an uninformative message. To find out what is the reason for this exception, we should try to reproduce the situation ourselves and check the content of the response. Sometimes it's very difficult.

Solution I'd propose

Maybe add response content to text of UnexpectedStatus exception? Or add some flag that allows us to show the contents of the response when we receive an unexpected status code?

[harabat]

I made PR #989 to implement this feature in its simplest form, by adding the response content to the error message.

[dbanty]

Released with 0.19.0, thanks!