[vc/nodepool subcmd] support --affinity for add operation

[fuweid]

Background

Currently. nodepool is managed by kwok controller which is running as pod.
kperf runner sub-command might use more network resource, which could impact kwok-controller in that same node.
Ideally, we can deploy kwok-controller into dedicated nodes which have specific labels and only are used for kwok-controllers.

Plan

This feature depends on [helmcli] support YAMLValuesApplier helper function feature.

Add --affinity flag in add sub-command. This flag is string slice type. https://pkg.go.dev/github.com/urfave/cli#StringSliceFlag

Each input's format is key=value1,value2,value3,.... The value is array using , as seperator.
Based on #17, the virtualcluster/nodes helm chart is using controllerNodeSelector map value to render node affinity.

kperf/manifests/virtualcluster/nodes/templates/statefulsets.tpl

Lines 17 to 31 in 636d5a4

	{{- if .Values.controllerNodeSelectors }}
	affinity:
	nodeAffinity:
	requiredDuringSchedulingIgnoredDuringExecution:
	nodeSelectorTerms:
	- matchExpressions:
	{{- range $key, $values := .Values.controllerNodeSelectors }}
	- key: "{{ $key }}"
	operator: In
	values:
	{{- range $values }}
	- {{ . }}
	{{- end }}
	{{- end }}
	{{- end }}

The add sub-command should construct inputs into the following YAML value and use YAMLValuesApplier to render:

controllerNodeSelector:
  key1:
     - value1
     - value2
     - value3
  key2:
     - value1
     - value2