dhi guides: deploy Docker Hardened Images on OpenShift (#24358)

<!--Delete sections as needed -->

## Description

This guide explains how to deploy Docker Hardened Images in OpenShift
environments. It covers Security Context Constraints (SCCs), arbitrary
user ID assignment, file permission requirements, and best practices for
both runtime and development image variants.


<!-- Tell us what you did and why -->

Added new guide: content/guides/dhi-openshift.md

## Related issues or tickets


Supersedes #24293 (closed due to fork deletion)

<!-- Related issues, pull requests, or Jira tickets -->

## Reviews

<!-- Notes for reviewers here -->


Previously reviewed and approved by @dvdksn in #24293
@craig-osterhout was requested for review before the PR was closed
No content changes from the previously approved version
<!-- List applicable reviews (optionally @tag reviewers) -->

Author: ajeetraina