Add `:connect_timeout`

[wojtekmach]

Mirror Postgrex.

[wojtekmach]

Ref: xerions/mariaex#172 (review)

[wojtekmach]

We've added :connect_timeout and hardcoded handshake socket receive timeout to be 5000ms. In the future we might add configurable :handshake_timeout using timers similar to Postgrex's.