Separate DEB/RPM build and sign + publish

[BenTheElder]

What type of PR is this?

/kind cleanup

What this PR does / why we need it:

• Ensures we don't partially publish Packages after completing builds of Debians then failing to build RPMs, making it much easier for operators to resume the script (vs previously having to manually editing the script)
• Makes it possible to run the build, sign + publish steps of package publishing independently
• Cleans up the bash a bit, to follow better practices (DRY, no dependency on $(pwd) of the calling environment being the repo root)

Which issue(s) this PR fixes:

Special notes for your reviewer:

THIS IS BEST REVIEWED COMMIT BY COMMIT

I've prepared this PR so the first commit simply makes two additional copies of k8s-rapture.sh

Then subsequent commits transform them, so you can see which lines are actually added or removed to each step, instead of having to read totally net-new bash files (most of the script lines are exactly as written in the combined k8s-rapture they came from, the changes to fix those are broken down).

Does this PR introduce a user-facing change?

NONE

[BenjaminKazemi]

Thanks for making these changes Ben!
/lgtm

[BenjaminKazemi]

/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: BenjaminKazemi, BenTheElder

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