Update openbao to v0.19.0

What does this MR do?

• Bumps the openbao subchart from 0.18.1 to 0.19.0, which moves OpenBao from v2.5.5-gitlab2 to v2.6.2-gitlab1
• GitLab.com has been running v2.6.2-gitlab1

Related issues

• Relates to gitlab-org/gitlab#608229 (closed)
• OpenBao chart release - https://gitlab.com/gitlab-org/cloud-native/charts/openbao/-/releases/v0.19.0
• OpenBao chart MR - gitlab-org/cloud-native/charts/openbao!77 (merged)

Author checklist

For general guidance, please follow our Contributing guide.

Required

For anything in this list which will not be completed, please provide a reason in the MR discussion.

• Merge Request Title and Description are up to date, accurate, and descriptive.
• MR targeting the appropriate branch.
• MR has a green pipeline.
• Documentation created/updated.
  • Not needed, no values or behaviour change in this chart
• Tests added/updated.
  • Not needed for a dependency bump. Existing OpenBao specs pass locally
• Have you validated that your change works end-to-end on a real cluster deployment?
  • Describe how you did it in a comment.
• Equivalent MR/issue for omnibus-gitlab opened.
  • Not applicable, omnibus does not ship OpenBao
• When ready for review, MR is marked as ready (not a draft) and assigned to a reviewer.

Reviewers checklist

• As soon as you begin reviewing, select Start a review on your first comment so the MR shows Reviewer started review.
• MR has a green pipeline on https://gitlab.com/gitlab-org/charts/gitlab.
• Consider downstream impact to the Operator, as per evaluating impact from changes to GitLab chart.