🌱 Refactor generate-codegen

[lentzi90]

What this PR does / why we need it:

This commit changes how to run and build codegen. Instead of using a script inside the openapi-gen package, we now build and call the binary directly. This avoids issues where the upstream package is incompatible with the go version we use (as seen currently on release-0.12).

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):

Related to (but does not fix) #2742
We need to do a manual backport of this to fix that issue.

Special notes for your reviewer:

1. Please confirm that if this PR changes any image versions, then that's the sole change this PR makes.

TODOs:

• squashed commits
• if necessary:
  • includes documentation
  • adds unit tests

/hold

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[lentzi90]

/hold cancel
/cc @smoshiur1237 @adilGhaffarDev
Can you check if this makes sense?
The reason I want this merged is that the current way of doing this has broken tests on release-0.12 (#2742). Main is unaffected at this time, but it would not make sense to do code generation differently on a release branch than on main. So I want to refactor here on main and then backport (see #2762) to fix the release branch.

[smoshiur1237]

This makes more useful and it is not dependent on the incompatible go version.
Thanks for this addition
/lgtm

[adilGhaffarDev]

LGTM

[lentzi90]

Thank you both!
/approve

[k8s-ci-robot]

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