Add option for running in "monolithic" (all) mode

[TaylorMutch]

trafficstars

I would love to be able to run Cortex in smaller environments in a "monolithic" mode, so I can stand up integration tests without having to specify an entire distributed stack.

We could add the option to specify a "mode", and keep the current distributed mode as the default.

[stale[bot]]

This issue has been automatically marked as stale because it has not had any activity in the past 30 days. It will be closed in 15 days if no further activity occurs. Thank you for your contributions.

[TaylorMutch]

I'm still interested in contributing this