Move relevant code from controlplane to util package

[dlipovetsky]

Some functions (e.g. that fetch or filter Machines) should be moved from the controlplane package to the util package.

(Issue came out of this discussion: #2037 (comment))

[fejta-bot]

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/lifecycle stale

[detiber]

/lifecycle frozen

[vincepri]

@benmoss this might be worthwhile to explore this cycle

[vincepri]

/milestone v0.3.x

[benmoss]

/assign

[vincepri]

/milestone v0.3.6

[benmoss]

@dlipovetsky is this still relevant? We now rely a lot on the FilterableMachineCollection in KCP, would that be what we want to move to util?

[vincepri]

/help
/priority backlog
/milestone v0.3.x

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In response to this:

/help
/priority backlog
/milestone v0.3.x

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[dlipovetsky]

I think this got done, but the issue wasn't closed.

[CecileRobertMichon]

Actually did this in #4160