Create installation and operation documentation for OpenBao

Summary

Provide user facing documentation for operating the OpenBao chart

Success criteria

Documentation exists for:

• Installation
  • required prerequisites including any manual steps, DB setup and expectations, secrets, unsealing https://gitlab.com/gitlab-org/charts/gitlab/-/blob/master/doc/development/openbao/_index.md?ref_type=heads#setup-gitlab-and-openbao
  • link to resource considerations and expected specs guidance ( output of gitlab-org/gitlab#568356)
  • available configuration settings, examples - https://gitlab.com/gitlab-org/charts/gitlab/-/blob/master/doc/development/openbao/_index.md?ref_type=heads#configuration
  • scaling guidance (note about active-passive model) HPA tuning + HA,
  • integration with monitoring https://gitlab.com/gitlab-org/charts/gitlab/-/blob/master/doc/development/openbao/_index.md?ref_type=heads#monitoring
  • TLS support
• Upgrade - downtime/ZDU https://gitlab.com/gitlab-org/charts/gitlab/-/blob/master/doc/development/openbao/_index.md#limitations
• Backup/restore https://gitlab.com/gitlab-org/charts/gitlab/-/blob/master/doc/development/openbao/_index.md?ref_type=heads#database-backup
• Geo status support
  • Documented as a limitation for now https://gitlab.com/gitlab-org/charts/gitlab/-/blob/master/doc/development/openbao/_index.md#limitations
• Known limitations and risks (ex. seal outage?) / troubleshooting
  • https://gitlab.com/gitlab-org/charts/gitlab/-/blob/master/doc/development/openbao/_index.md#limitations

See #18 (comment 2729236525)

Known references

• gitlab-org/gitlab!199731 (merged)
• https://gitlab.com/gitlab-org/charts/gitlab/-/blob/master/doc/development/openbao/_index.md?ref_type=heads
• gitlab-org/charts/gitlab!4495 (merged)