Bump openbao chart version to 0.13.0

What does this MR do?

Bumps the OpenBao chart version to 0.13.0 to support AWS KMS unsealing and adds documentation. This enables the GitLab Environment Toolkit to use AWS KMS for OpenBao key management, as introduced in gitlab-org/gitlab-environment-toolkit!1815 (merged).

Related issues

• gitlab-org/gitlab-environment-toolkit!1815 (merged) - OpenBao AWS KMS unseal support

Author checklist

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Required

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• 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.
• Tests added/updated, and test plan for scenarios not covered by automated tests.
• Equivalent MR/issue for omnibus-gitlab opened.

Reviewers checklist

• 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.