Add CompressWithoutPreservingPath to tar package

[xmudrii]

What type of PR is this?

/kind feature

What this PR does / why we need it:

The default way the tar.Compress function works is that we preserve the path between tarFilePath and tarContentsPath directories inside the archive.

This might not work well if tarFilePath and tarContentsPath are on different levels in the file system (e.g. they don't have a common parent directory). In such case we can disable preserveRootDirStructure flag which will make paths inside the archive relative to tarContentsPath.

The test case of this newly-added function describes what I'm trying to accomplish.

Special notes for your reviewer:

I don't like CompressWithoutPreservingPath function name and I'm very welcome to any ideas. 🙃

Does this PR introduce a user-facing change?

Add `CompressWithoutPreservingPath` function to the `tar` package

/assign @saschagrunert @cpanato
cc @kubernetes-sigs/release-engineering

[cpanato]

/lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: cpanato, xmudrii

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