new feature: have align-deps tell you which capabilities you could add

[kelset]

This started as a side-conversation around #932

Basically, it'd be great if align-deps, when the CLI command is run, could check all your dependencies, check which ones you have in the "capabilities" config in your package.json, and tell you which other capabilities you could add that are covered by the tool. Ex. if you have "react-dom" in your dependencies but not as capability, it could let you know that the capability for it exists - so that you don't need to rely on the vigilant flag to make sure that ALL your dependencies are correct :)

This would also highly help developers when upgrading to newer versions of align-deps; right now the only way to know if some capability has been added is to manually check the changelog or the main table in the README. So there's a high risk of folks not knowing that ex. react-dom has a capability dedicated to it right now.