add BOSH Release tarball reading utilities

[crhntr]

This adds some utilities for reading BOSH release manifests (release.MF) from tarballs.

I refactor the builder and acceptance tests to use this to show that this makes sense as a place for these utility functions. My main intent for adding them was to use them in the kiln buildpacks.

[cf-gitbot]

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[jaristiz]

Like the refactor to the release package, found it confusing when using github.com/kiln/pkg/tile package in other projects.

[crhntr]

I agree renaming it would make it make more sense. I also don't like that I take the "tile" identifier; it is such a good variable name. Maybe tilerelease? Unfortunately, "release" is such an overloaded term.

[dtimm]

Why add this to kiln specifically? I think it would make more sense as a separate repository that is used in kiln rather than included wholesale. Since it isn't used (yet), could the PR wait until the functionality is needed?

[crhntr]

We do use these utilities in kiln bake.

I have found these utilities to be useful in buildpacks and so I wanted to put these utilities somewhere open source. They used to be in PPET but I have found using that even for internal projects not easy. GOPRIVATE is not fun to set up in CI.

After thinking about your comment. I think these functions make more sense in cargo because they operate on the BOSH Release Tarballs within the tiles. Also it might make sense to add the bosh release package data to the Kilnfile.lock.