Re-add the Client constructor methods, but deprecate them
Re-add the Client constructor methods, but deprecate them

These were removed in https://github.com/serenity-rs/serenity/commit/56fe660b789ab1ac2aad9d75b4d3add39abf1cf8 as they duplicated code from `new`, and have therefore been replaced by `new_with_extras`.

But the replacement doesn't justify their *whole* removal. Instead, they'll serve as shorthands for using
the new method.

acdenisSK/serenity,Flat/serenity