Feat add tcp keepalive configuration

[bburnichon]

I came across the same issue as #853 (albeit with another keepalive value). It would then also allowing to fix #854

This PR solves it via adding a way to configure tcp keepalive to whatever needed.

For tls, you would need to change the configuration before switching to tls configuration.

[jq-rs]

Configurable keepalive is way better than any default value, looks good!