ktls: alert/handshake data

[toidiu]

This task involves sending alert and handshake record types from ktls. We will not be sending handshake types for the MVP. KeyUpdate support will be added later when TLS1.3 support is added.

Here is a WIP on how alert integration might look like. Relevant files are s2n_shutdown.c, s2n_alerts.c

We want to integrate from s2n_shutdown.c. I added a new method s2n_alerts_get_error_or_close_notify since the existing method s2n_alerts_write_error_or_close_notify wrote a record.

These are all the connection state variables that need to be updated: https://github.com/aws/s2n-tls/pull/4162/files#diff-732fdef032104706c8a36a45efd7c4098fed24bcec6906b78c81b1bfc9e61eaeR298-R325