Consider renaming `path` source property in spec

[adamperlin]

Sources can have an output path property, such as:

    gomods: # This is required when the build environment does not allow network access. This downloads all the go modules.
    path: /build/gomodcache # This is the path we will be extracing after running the command below.
    image:
      ref: mcr.microsoft.com/oss/go/microsoft/golang:1.21
      cmd:
     ...

However, in my opinion path here is a little ambiguous in the spec for new users of dalec, without the added comment that path is where we are extracting from. I would propose changing the name of path to target_path or something similar, to make it clearer that the state which is extracted from the source is what is under the path. @cpuguy83 @pmengelbert do you have any thoughts?