Support independent fixup scripts

[72636c]

As best practices evolve, it's easy for existing repos to fall behind. Having a command that allows you to browse suggestions or automatic fixers would make upkeep a simpler process. These shouldn't require much buy-in to the base skuba templates either as we know that teams will deviate.

A reasonable starting point would be the existing monolithic skuba configure command. Breaking that command up into multiple separate submodules that would make initial configuration a lot less hamfisted while also enabling this exact use case.

Examples of potential fixups include:

1. Upgrading to the latest Node.js version
2. Adopting serverless-plugin-canary-deployments

There's also opportunity to roll glaring issues into custom linting rules that are packaged up into skuba lint. That would give us the power to break CI if the issue is deemed serious enough.

[samchungy]

I believe #1382 resolved this