Add configuration for startRecordSessionCmd

[rmccue]

When logging is enabled, ssm-agent uses script to record the session:

https://github.com/aws/amazon-ssm-agent/blob/57bb3c6935e12dce8cf662afffc435516d8dc3c3/agent/session/shell/shell_unix.go#L53

It would be great to be able to reconfigure this to use custom commands instead, to allow for more detailed recordings like asciinema or to add custom log entries.

[ziwangj]

Thank you for bringing this to our attention. We have noted your request.