Add "model" macro to simplify model definitions

[tjkirch]

This removes a lot of repetitive attributes and type modifiers through the use
of a attribute-style procedural macro applied to our model structs.

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See the README for the exact changes the macro makes. See the models for how simple they are now :)

Testing done:

I used cargo-expand to compare the generated model package before and after. The only changes were whitespace, ordering of attributes, the new use of model-derive, and the intentional removal of the rustfmt::skip that's no longer needed.

I built and launched an aws-k8s AMI, confirmed all services running, and the API showed all settings. A pod ran OK.

I built and launched an aws-dev AMI, it was running, showed all settings, and a Docker container ran OK.

[tjkirch]

(The pushes clean up two typos)

[tjkirch]

This push fixes a typo caught by bcressey.

[iliana]

I like this. Removing the Option<T> in all the types would certainly be confusing if I hadn't seen the #[model] attribute before and I'm trying to write code that uses those fields, but I'm not sure how to resolve that.