main.go in each applet carrying too much functionality

[softwareplumber]

In each applet (estuary, estuary-shuttle, etc...), main.go:

• performs command line and environment processing
• post PR-141 will be processing configuration files
• sets up state, database connections, resource management, and kicks of the main application processing

dividing these responsibilities between files will help keep the estuary codebase manageable and improve testability by separating concerns. Suggest that main.go handle processing command line and config, setting up a config object with is then handed over to an applet.go (or whatever name is deemed appropriate). This would also be a useful first step toward consolidating the command line processing for the different applets into a single file.

[softwareplumber]

Related issue #142

[corinne-antonia]

@alvin-reyes Can you help me put together a plan for some of these refactors? It seems like we have a bunch of ideas for separation of concerns. I think we could combine all the ideas into a single plan and get it approved by @whyrusleeping. It also seems like a great opportunity for someone to get get to know how estuary works.