[8.18] (backport #8320) ci: update all n1-standard-8 type runners to n2-standard-8

[mergify]

What does this PR do?

This PR updates all Buildkite pipeline steps that were previously using n1-standard-8 GCP machine types to instead use n2-standard-8.

The following pipeline YAML files were updated:

• .buildkite/bk.integration.pipeline.yml
• .buildkite/pipeline.elastic-agent-helm-charts.yml
• .buildkite/pipeline.integration-test-matrix.yml

Why is it important?

The n1 machine series is deprecated and offers worse performance and price efficiency compared to the n2 series. As noted in the review of a prior PR, using n2-standard-8 helps prevent resource limitations and improves overall CI stability and performance. This change ensures consistency across all CI steps and aligns with best practices for machine type selection in GCP (context here).

Checklist

• I have read and understood the pull request guidelines of this project.
• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works
• I have added an entry in ./changelog/fragments using the changelog tool
• I have added an integration test or an E2E test

Disruptive User Impact

None. This is a CI-only change and does not affect the behavior of the Elastic Agent or its packaging. No user-facing configuration or interface is impacted.

How to test this PR locally

These changes affect the CI configuration and will be automatically exercised by Buildkite when the pipeline runs.

Related issues

• Follows up on review feedback in a previous PR: use of n2-standard-8 for better performance and consistency

  ---

  This is an automatic backport of pull request ci: update all n1-standard-8 type runners to n2-standard-8 #8320 done by Mergify.

[mergify]

Cherry-pick of 349cbc7 has failed:

On branch mergify/bp/8.18/pr-8320
Your branch is up to date with 'origin/8.18'.

You are currently cherry-picking commit 349cbc776.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   .buildkite/pipeline.elastic-agent-helm-charts.yml
	modified:   .buildkite/pipeline.integration-test-matrix.yml

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   .buildkite/bk.integration.pipeline.yml

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

[pkoutsovasilis]

requires this #8308

[elastic-sonarqube]

Quality Gate passed

Issues
0 New issues
0 Fixed issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
No data about Duplication

See analysis details on SonarQube

[dliappis]

LGTM