[v2.12.0] Ensure CI/documentation reflect changes to default admin credentials

[derek-ho]

Background

Previously, when installing the security plugin demo configuration, the cluster was spun up with the default admin credentials, admin:admin. A change was made in main and backported to 2.x for the 2.12.0 release, which now requires an initial admin password to be passed in via the environment variable OPENSEARCH_INITIAL_ADMIN_PASSWORD. This will break some CI/testing that relies on OpenSearch to come up without setting this environment variable. This tracking issue is to ensure compliance with the new changes.

Coming from: opensearch-project/security#3624

Acceptance Criteria

• All documentation references to the old default credentials admin:admin are removed
• Ensure that CI/testing is working with main and 2.x branches

[wanglam]

Hi @derek-ho , Thanks for your suggestion. We don't hard code any admin:admin as default credentials in our codebase. Could we marked the All documentation references to the old default credentials admin:admin are removed to complete? Just find there is another PR in FT repo. This PR will update credentials in .github/workflows/release-e2e-workflow-template.yml, the CI workflow of ml-commons-dashboards use the same template. I think the CI will be fixed after PR merged.

[derek-ho]

@wanglam if the CI is working fine on 2.x/main and no credentials are present I think we can close this. Please feel free to do so, I did a quick search and didn't find anything.