fix: use common pod selector in metrics service

[taraspos]

Issue #, if available:

• Add metrics with, at least, success rate #13

Description of changes:

Currently metrics service selector doesn't work, because it uses label app which is NOT assigned to pods.
This change will use {{- include "eks-pod-identity-agent.selectorLabels" . | nindent 4 }} instead, same as daemon set does.

Code refernces:

• eks-pod-identity-agent/charts/eks-pod-identity-agent/templates/daemonset.yaml

  Lines 11 to 18 in af723f6

  	selector:
  	matchLabels:
  	{{- include "eks-pod-identity-agent.selectorLabels" . | nindent 6 }}
  	template:
  	metadata:
  	labels:
  	{{- include "eks-pod-identity-agent.selectorLabels" . | nindent 8 }}
  	{{- with .Values.podAnnotations }}

• eks-pod-identity-agent/charts/eks-pod-identity-agent/templates/_helpers.tpl

  Lines 46 to 52 in af723f6

  	{{/*
  	Selector labels
  	*/}}
  	{{- define "eks-pod-identity-agent.selectorLabels" -}}
  	app.kubernetes.io/name: {{ include "eks-pod-identity-agent.name" . }}
  	app.kubernetes.io/instance: {{ .Release.Name }}
  	{{- end }}

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[taraspos]

@micahhausler @kmala would appreciate if you could take a look at this one as well :)