Add support for Red Hat openshift compatible image

[Rkabra7]

Description

This PR adds native Red Hat UBI/OpenShift image support to Boundary by consolidating the previous Dockerfile.openshift setup into the main Dockerfile as a dedicated ubi stage and integrating it with the standard CI/CD release pipeline.

Changes

Added a ubi stage based on ubi9/ubi-minimal
Added Red Hat certification labels, license files, non-root user, and OpenShift-compatible permissions
Introduced a new OpenShift entrypoint handling arbitrary UID support and permission checks
Added CI workflow to build and push multi-arch (amd64/arm64) UBI images to the Red Hat Connect registry
Registered UBI image tarballs as release artifacts
Updated .dockerignore to include LICENSE in build context

Testing

Validated successfully using a temporary build-redhat-test.yml workflow before merge.

PCI review checklist

• I have documented a clear reason for, and description of, the change I am making.
• If applicable, I've documented a plan to revert these changes if they require more than reverting the pull request.
• If applicable, I've documented the impact of any changes to security controls.
  Examples of changes to security controls include using new access control methods, adding or removing logging pipelines, etc.

[hashicorp-cla-app]

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• Rkabra7
• Raghav Kabra

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[hashicorp-cla-app]

Thank you for your submission! We require that all contributors sign our Contributor License Agreement ("CLA") before we can accept the contribution. Read and sign the agreement

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[moduli]

Could you also sign the CLA? https://cla.hashicorp.com/hashicorp/boundary?pullRequest=6700