Update the quickstart guide for using Elastic Agent in a Kubernetes cluster

[vishaangelova]

This PR updates the Quickstart: Monitor your Kubernetes cluster with Elastic Agent guide with the following changes:

• Updates the Prerequisites section
• Updates the Serverless use case to use helm, and adds information about the helm command
• Removes references to kubectl from the introduction as this command is no longer used for the Serverless use case
• Adds new sections:
  • Uninstall Elastic Agent from the Kubernetes cluster
  • Troubleshooting
  • Limitation (a disclaimer for air-gapped environments that provides resources for running Elastic Agent in an air-gapped environment)

Closes https://github.com/elastic/docs-content-internal/issues/147

Preview

https://docs-v3-preview.elastic.dev/elastic/docs-content/pull/2433/solutions/observability/get-started/quickstart-monitor-kubernetes-cluster-with-elastic-agent

[github-actions]

🔍 Preview links for changed docs

• solutions/observability/get-started/quickstart-monitor-kubernetes-cluster-with-elastic-agent.md

[benironside]

This looks great! Left some suggestions for your consideration

[flash1293]

Can't comment too much on the details, can we rope someone from the ingest team in to review this?

[eedugon]

Looks very good, great work!!!

[vishaangelova]

@pkoutsovasilis and @eedugon I’ve updated the PR based on your suggestions. Could you have a look?

[eedugon]

LGTM! Just added 2 minor suggestions :)

[gbamparop]

Can't comment too much on the details, can we rope someone from the ingest team in to review this?

Same here about the helm and kubectl details

The other changes look good, thanks!

[benironside]

LGTM! 😄