Upgrade to gitlab-openbao:v2.6.2-gitlab1

Why this MR ?

• Part of gitlab-org/gitlab#608229 (closed)
• OpenBao v2.6.2-gitlab1 is released and the CNG gitlab-openbao images for it are published
• GitLab.com has been running it on staging and production since 2026-09-23
• Self-managed chart installs are still on v2.5.5-gitlab2

What does this MR do ?

• Bump appVersion to v2.6.2-gitlab1 and chart version to 0.19.0
• Installs using the opt-in awskms seal will log a deprecation warning at startup, since OpenBao v2.7.0 drops the built-in cloud KMS seals for external plugins. The default static seal is not affected

Testing

• The 2.6.2 version image was deployed to a self managed instance on GCP and functionality was tested and verified

References

• Issue - gitlab-org/gitlab#608229 (closed)
• OpenBao release - https://gitlab.com/gitlab-org/govern/secrets-management/openbao-internal/-/releases/v2.6.2-gitlab1
• CNG MR - gitlab-org/build/CNG!3090 (merged)
• GitLab.com rollout MR - https://gitlab.com/gitlab-org/govern/secrets-management/secrets-manager-runway/-/merge_requests/29