Initial GitLab Secret Manager (OpenBao) support

What does this MR do?

The MR adds Experimental initial GitLab Secret Manager (OpenBao) support

• Cloud Native Hybrid support only with Chart (no Operator)
• Only for external DB installations (cloud provider DBs, not Omnibus PG cluster)
• Deployed on Supporting node pool
• OpenBao DB is created as separate logical DB on main PG
• Limited Geo support aligning with GitLab Secret Manager feature Geo support status

Relevant docs: https://gitlab.com/gitlab-org/cloud-native/charts/openbao, https://docs.gitlab.com/charts/charts/openbao/

Feature additions:

• Required configurations from user are OpenBao URL, db password for OpenBao DB, and Chart specific deployment configs - replicas, CPU and memory limits
• TLS is enabled if URL contains https
• Optional support for Unseal keys secret allowing users to provide values for secret - required for Geo installation to sync the key between sites
• Monitoring is enabled with PodMonitor setting
• The MR also adds OpenBao molecule scenario for local testing

Related issues

https://gitlab.com/gitlab-org/gitlab-environment-toolkit/-/work_items/1138+

Author's checklist

When ready for review, the Author applies the workflowready for review label and mention @gitlab-org/software-delivery/get-maintainers:

• Merge request:
  • Corresponding Issue raised and reviewed by the GET maintainers team.
  • Merge Request Title and Description are up-to-date, accurate, and descriptive
  • MR targeting the appropriate branch
  • MR has a green pipeline
  • MR has no new security alerts in the widget from the Secret Detection and IaC Scan (SAST) jobs.
• Code:
  • Check the area changed works as expected across all expected permutations.
    • Testing notes are available at https://gitlab.com/gitlab-org/gitlab-environment-toolkit/-/issues/1138#note_2832402731
  • Check that the changes work across upgrades.
  • Documentation created/updated in the same MR if applicable - No documentation due to Experimental status

Closes #1138