Configurable DNS resolve timeout

cpp-driver [exposes API](https://github.com/scylladb/cpp-driver/blob/fa0f27069a625057984d1fa58f434ea99b86c83f/include/cassandra.h#L2047) to configure [DNS resolution timeout](https://github.com/scylladb/cpp-driver/blob/fa0f27069a625057984d1fa58f434ea99b86c83f/src/resolver.hpp#L85). Let's do the same.