hello. I use tokio-postgres a lot.

Thing I want to do

I would like to customize interval and retries when keepalive is turned on.
Therefore, I propose to make it possible to specify the keepalive interval and retries in this pull-request.

Features to add

Previously, the only keepalive parameter waskeepalives_idle. This time, addkeepalives_interval andkeepalives_retries.keepalives_interval is available on neither Redox nor Solaris.keepalives_retries is available on neither Redox, Solaris nor Windows. This constraint aligns with that ofsocket2::TcpKeepalive.

Implementation

I thought that addingkeepalives_interval andkeepalives_retries blindly would increase the number of arguments for theconnect_socket::connect_socket() and make the source code messy.
So I defined a new structKeepaliveConfig. It does not publish outside the crate.
As an alternative, I considered puttingsocket2::TcpKeepalive inConfig, but I rejected it becausesocket2::TcpKeepalive has no getter method and is incompatible withConfig.