ngrok Agent: add an AutoUpdate option

[russorat]

From @SecretRecipe: inconshreveable/ngrok#917

Is there an autoupdate: true option available for the config?

If not; can we get one?

[russorat]

Thanks for the issue. The check for a new version is available but the agent will not automatically restart to pick it up.

Do you need to specify a specific time for the restart to happen? We could just be smart and try to do it when we haven't seen a connection for a period of time.

The way i imagine this would work would be:

• if update_check is true
  • if restart_on_update (new flag) is set to true (default false)
    • install the latest ngrok agent update and restart

This flag would be specific to the ngrok agent, not the sdks.

I would not expect this to work across major version upgrades (v3 to v4 for example) but minor and patch updates would probably be fine.