Reconnect to Doppler after network failure when using --watch

[apazzolini]

Prior to this PR, if a client is using the --watch flag and loses connectivity to the Doppler API (either because they lost internet or the service they were connected to went down), the process started by doppler run would continue running but never be restarted.

This PR will now detect connectivity failures and handle reconnection. When reconnecting, the process will only be restarted if secrets have indeed changed; if no secrets were changed, the pre-existing process will continue running.

Closes ENG-8855