[JENKINS-72112] Allow merge strategy inheritance in PodTemplates

[georgblumenschein]

Ticket: https://issues.jenkins.io/browse/JENKINS-72112

Note

This Pull Request is taken from #1448 and the changes done there!
I was not quite sure what the workflow in such cases is, I could also open a PR on the fork so that the first forker can update the PR here, I just assumed it is simpler this way.

Testing done

Testing done in #1448, I am fixing (at least I try ;-) ) the automated tests that prevent it from merging.

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[georgblumenschein]

Two notes:
I had to rebase to get the pipeline green, meaning it looks like I did that, but credit for 99% of the work goes to @vivienfricadelamadeus
Failing test seems to be flaky with a problem pulling the busybox image, all checks ran through before I squashed them, so a retrigger should resolve this.