Compress k0s binary using UPX

[twz123]

Description

Make this configurable via Make variables.

This is a PoC based on #5468, to see if it is generally possible and to have something to tinker with. CI seems to be passing. The size reduction is about 25% for the linux-amd64 executable, and over 30% for the windows-amd64 executable.

I did some highly scientific ^^ benchmarks using time ./k0s on my machine, to compare startup times of the compressed and uncompressed versions of the executable. For me, compression added around 420 ms of startup latency.

See:

• A k0s binary compressed with upx won't start #5468

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update

How Has This Been Tested?

• Manual test
• Auto test added

Checklist:

• My code follows the style guidelines of this project
• My commit messages are signed-off
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules
• I have checked my code and corrected any misspellings