Add a `SKIP_ORION` option to the start script

[thesan]

This is just a DX thing but I keep on adding this to the start script.

Here's why: only Atlas usues Orion, and a lot of the work on Atlas is done using a playgrounds ATM. OTOH when working on Orion directly IMO it's easier to run Orion from the local repository not from the monorepos.