feat(jdk21) Use Liberica official build for linux/arm/v7

[gounthar]

As discussed in #772, the community has decided to discontinue supplying arm32 docker images since Temurin does not plan to release them.
Through this PR, I aim to present an alternative by using Liberica JDK binaries.
I'm not suggesting we should make this change; I'm merely proposing that we could, considering the minor changes required in our repository.

However, it's essential to note that while the changes in our repository may be minor, the impact on end-users could be significant.
Should we abandon arm32 images altogether, or should we consider switching to another JDK vendor for just this platform?
I don't have a definitive answer.

Please view this PR as a proof of concept rather than a desperate plea to reinstate arm32 support.
If the community were to accept this proposal, I would be willing to maintain it.

While I still hold hope that Temurin will eventually resume regular arm32 builds for JDK21+, it's essential to acknowledge the constraints faced by open-source projects, including limited time, hardware, and resources.

I realize that I should have split the PR into two parts, as the updatecli manifest should fail due to a missing variable in the master branch.

Thank you for your time.

Testing done

make ARCH=arm/v7 build-agent_debian_jdk21_liberica
updatecli diff --debug --config ./updatecli/updatecli.d/jdk21-arm32.yaml --values ./updatecli/values.github-action.yaml

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