This change implements the same preview behavior we have for
cloud stacks, in pkg/backend/httpbe, for local stacks, in
pkg/backend/filebe. This mostly required just refactoring bits
and pieces so that we can share more of the code, although it
does still entail quite a bit of redundancy. In particular, the
apply functions for both backends are now so close to being
unified, but still require enough custom logic that it warrants
keeping them separate (for now...)
This simply refactors all the display logic out of the
pkg/backend/filestate package. This helps to gear us up to better unify
this logic between the filestate and httpstate backends.
Furthermore, this really ought to be in its own non-backend,
CLI-specific package, but I'm taking one step at a time here.
This renames the backend packages to more closely align with the
new direction for them. Namely, pkg/backend/cloud becomes
pkg/backend/httpstate and pkg/backend/local becomes
pkg/backend/filestate. This also helps to clarify that these are meant
to be around state management and so the upcoming refactoring required
to split out (e.g.) the display logic (amongst other things) will make
more sense, and we'll need better package names for those too.
