Helm Chart: make default resources empty so users can omit cpu request/limit

## Description The [Helm chart](https://github.com/kubernetes-sigs/descheduler/tree/master/charts/descheduler) currently sets default container resources (including CPU request/limit). This makes it impossible to configure only memory (or to "unset" CPU limits) via values overrides, because Helm values merging won't remove keys from the chart's default map. ### Current behaviour [[link](https://github.com/kubernetes-sigs/descheduler/blob/b6e81fdd4b508f3abaf75e53d28c90b69455bf29/charts/descheduler/values.yaml#L17)] Chart defaults include CPU, e.g.: ``` resources: requests: cpu: 500m memory: 256Mi limits: cpu: 500m memory: 256Mi ``` If a user tries to omit CPU by removing it from their override file, or setting cpu: "", Helm's merge results in CPU being retained from the chart defaults (or producing an invalid quantity). ### Expected behavior Chart should not force CPU requests/limits by default. Users should decide their own sizing. ### Why this matters Many clusters rely on defaults (or Vertical Pod Autoscaler, LimitRanges, etc.) and do not want to pin CPU limits for this workload. With current defaults, you can't express "set memory but don't set cpu" using values alone. ### Proposed change Change chart values.yaml default from a populated map to an empty one: ``` resources: {} ```