Add openbao.jwt_audience

What does this MR do?

Adds support for configuring OpenBao JWT audience in the GitLab Helm chart. This enables proper JWT authentication in GitLab Geo deployments where secondary sites may have different OpenBao URLs.

Related issues

Closes gitlab-org/gitlab#571099 (closed)

Changes

• Adds openbao.jwt_audience Helm value to allow independent configuration of JWT audience from the OpenBao URL
• Enables flexible audience validation in multi-site Geo deployments
• Maintains backward compatibility by defaulting to the OpenBao URL when not specified

Configuration Example

For Geo deployments with different OpenBao URLs per site:

openbao:
  url: https://openbao.site-specific.example.com:8200
  jwt_audience: https://openbao.shared.example.com:8200

Related MR

This is a follow-up to gitlab-org/gitlab!223741 (merged) which implements the core JWT audience functionality in GitLab.

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.