Feat: CLI `polywrap codegen` Command

[dOrgJelli]

I think the CLI interface should be:

polywrap codegen
polywrap build
polywrap deploy
polywrap infra
polywrap create
polywrap run

Where each command decides internally what projects it works with.

This PR consolidates the polywrap plugin codegen and polywrap app codegen commands into a single polywrap codegen command. Additionally it refines best-practices about what options should be defined in polywrap manifest files and which are provided on the CLI.

NOTE: see the todo file for WIP impl notes

TODO:

• [ ] option to override any property
• [ ] option to specify a override fragment yaml file

closes: #1153