feat: add addLabels utility

[mrliptontea]

Add a utility function that allows to add a set of labels to objects, including to their nested Pod templates.

Example use:

import { Helm } from "cdk8s";
import { addLabels } from "talis-cdk8s-constructs";

const helm = new Helm(chart, "helm-template", {
  repo: "https://aws.github.io/eks-charts",
  chart: "aws-load-balancer-controller",
  releaseName: "aws-load-balancer-controller",
  version: "1.6.1",
});

addLabels(helm.apiObjects, {
  "my-label": "my-value",
});

[talisaspire]

🎉 This PR is included in version 4.2.0 🎉

The release is available on GitHub release

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