Add backup config generation

[shreddedbacon]

This adds functionality to generate backup configuration

This is also a major update to the way that build values are sourced by moving everything that used to be spread over multiple files in the cmd package to be its own generator package now.
This should hopefully make it more obvious where build values are calculated. The idea of the generator package is to take all the inputs of a build and produce a set of values that can be passed to different components of the build, like ingress templating, or backup templating.

Eventually other templating packages can consume the values from the generator.