[ST] Re-factor applying NetworkPolicy with copying secrets

[see-quick]

We should refactor our current way of creating an auxiliary namespace, application of NP and copying of pull secret (in system tests) and follow the rule DRY.

KubeClusterResource.getInstance().createNamespace(CollectorElement.createCollectorElement(simpleClassName), Constants.TEST_SUITE_NAMESPACE);
NetworkPolicyResource.applyDefaultNetworkPolicySettings(extensionContext, Collections.singletonList(Constants.TEST_SUITE_NAMESPACE));
StUtils.copyImagePullSecrets(Constants.TEST_SUITE_NAMESPACE);

[im-konge]

Done in #9496