[FEAT shoot-grafter] - Use CopyLabels from Propagator

[Zaggy21]

Priority

(Medium) I'm annoyed but I'll live

Description

With Issue #30 the Greenhouse Propagator has been introduced to propagate labels.
Greenhouse issue 1792 introduced a new helper function for copying labels.
In ShootController use the new CopyLabels function instead of applying the propagation (which requires setting a label on Shoot resource).

Reference Issues

No response