Add exported Elasticsearch config and permissions test

What does this MR do and why?

• Adds exported Elasticsearch configuration to the project. It's good practice to track changes to this in Git, and it's also good to have a backup.
• Adds a test to validate permissions on the Elastic API key

Closes #139 (closed)

Screenshots, screen recordings, or links to review app

• Failing job: https://gitlab.com/gitlab-org/technical-writing-group/gitlab-docs-hugo/-/jobs/8094091228
  • The production key had overly-loose permissions (ability to read cluster health), and so it failed this test. This is good!
• Passing job: https://gitlab.com/gitlab-org/technical-writing-group/gitlab-docs-hugo/-/jobs/8094351845
  • After I adjusted the permissions on the key to replace cluster: ["all"] with the more restrictive cluster: ["post_behavioral_analytics_event"], the test now passes.

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

1. Configure a local GitLab Docs environment: https://gitlab.com/gitlab-org/technical-writing-group/gitlab-docs-hugo/-/blob/main/doc/setup.md.
2. Run the test with your existing key: make check-elastic-key-permissions. This should FAIL because your existing key ("hiru localhost") still has the cluster: ["all"] permission.
3. Adjust your localhost key to match the updated recommended permissions (copy from here): https://gitlab-docs-website.kb.us-central1.gcp.cloud.es.io:9243/app/management/security/api_keys/
4. Run the test again: make check-elastic-key-permissions. This should PASS
5. Make a new key that has no access control (leave "Control security privileges" off when creating the key). Run the test with this new, sketchy key: ELASTIC_KEY="abc123" make check-elastic-key-permissions. This should FAIL
6. Delete the test key

Merge request acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this merge request.