[infra] Improve cherry-pick workflow

[michelengelen]

This handles 2 things:

1. switches to a matrix approach to prevent consecutive PRs being opened. Now this workflow will not run a number of times for each PR merged, but rather once opening several cherry-pick PRs at once (if multiple targets are needed)
2. add the reviewers from the original PR to the cherry-pick PR to improve workflow even more

[michelengelen]

Sry @JCQuintas ... your comment resulted in an even better refactor! :P

Effectively removing the inheritance and assigning labels manually is better: https://github.com/carloscastrojumo/github-cherry-pick-action/blob/c980652a80bb76d11b6cdc38efb0a5cee28ff4e6/action.yml#L36-L39

That part is not documented in the README!