[FEATURE] Better support for development environments

Pipedream needs better support for development environments, where I can test changes e2e before shipping them to prod.

For example:

- Since HTTP interfaces and event sources live outside of projects, and point to the most recent production deployment, any changes I make to my workflow can't be tested e2e (outside of the builder / testing each step individually)
- Some flow control primitives (like `$.flow.rerun`, $.flow.suspend`) are "mocked" in development mode, and also difficult to test e2e without deploying my workflow to prod.