Background executions

[jahvon]

Enhancement Summary

Having the ability to execute workflows in the background (either triggered by an exec flag or scheduled as a cron task of sorts) can be helpful for many advanced use cases. This will require having a background process on the local machine that can handle this

Additional context

• https://github.com/kardianos/service seems to be a promising library for enabling this across platforms
• for the cron use case, there will need to be a new mechanism for scheduling executable runs. It would be nice to have that schedule pick up where it left off on computer restarts