[Refactor] adding strip_prefix, remap_paths, include_runfiles to pkg_zip

[grahamjenson]

I need to add include_runfiles attribute to pkg_zip and wanted to bring the pkg_tarandpkg_zip` rules closer to parity, so this PR adds the prepare_files method which both rules use to generate the list of added files.

Also updated the readme.

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[grahamjenson]

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[kigster]

Any word when this may be reviewed and merged?

[cfeckardt]

+1 would like to see this merged soon too.

[aiuto]

I think we should be trying for a more general solution that lets us define packages of files, how they remap, and if runfiles are included in rules distinct from tar, deb and rpm. Then the packagers should get all the requisite remapping info in a provider from that rule. #128 is trying to go down that path. Let's see how that plays out first.

[aiuto]

/cc @nacl @beasleyr-vmw

[sreeramaraju]

pkgfilegroup from #127 is not public visible. Is there a workaround to pass strip_prefix for pk_zip rule till work related to that is merged to upstream?

[davschne]

strip_prefix is now available for pkg_zip (see #221 above). I created the PR before I realized this one existed - whoops! I support this PR, though - it’s more complete and better leverages existing code. Could use some tests for remap_paths and include_runfiles.