arc: keep a values file's preferred node affinity when a profile has burst #143

arc_runner_placement returns an affinity.nodeAffinity with preferredDuringSchedulingIgnoredDuringExecution set to its own single term (keep off the burst nodes) whenever a profile has burst. The overlay is merged over the profile's values file with a recursive combine, which replaces lists, so a preferred term the values file sets under the same key is dropped without a message.

Repro: a profile with burst and a values file with template.spec.affinity.nodeAffinity.preferredDuringSchedulingIgnoredDuringExecution: [{weight: 100, preference: {matchExpressions: [{key: example.com/big, operator: In, values: ["true"]}]}}]. The rendered release values hold only the burst term.

A profile should be able to give preferred node terms that the role keeps beside its own, either as a profile key or by appending to the list when merging. The fixed-node preference for burst-less nodes has to stay first so it keeps its weight.