Close session when there is recording errors (Sync modes)

[gabrielcorado]

Closes https://github.com/gravitational/teleport-private/issues/369

Ensures SSH sessions are closed when there is a session recording error when sync recording is configured. The change consists of always setting the session recording mode to strict when recording is set to sync (node-sync and proxy-sync) and returning an error from the SessionWriter.

For the SessionWriter, we're adding a new config Strict to indicate whether it should return an error on RecordEvent. This way, we can keep the current behavior for every protocol using the session. Later on, we can update other protocols to handle this behavior correctly.

changelog: Fix SSH sessions not being closed when there is a recording error on sync recording modes.