Add RHDH skills volume support to LCORE container

[yangcao77]

What does this PR do?

PR title

Add RHDH skills volume support to LCORE

Summary

• Adds an emptyDir volume for RHDH skills.
• Uses an init container with quay.io/redhat-ai-dev/utils:latest to fetch the main branch of redhat-developer/rhdh-skills.
• Copies the repository’s skills/ contents into the shared volume.
• Mounts the volume at /app-root/skills in lightspeed-core.
• Keeps the mount writable so skill scripts can create or modify files when required.
• Makes the PostSync patch idempotent across repeated Argo CD syncs.
• Adds CI coverage for initial deployment and repeated synchronization.

Testing

• bash tests/helm/test-skills-volume.sh
• helm lint charts/rhdh --set okp.enabled=false
• ShellCheck
• git diff --check

No new LCORE image or long-running sidecar is introduced.

Which issue(s) does this PR fix

https://redhat.atlassian.net/browse/RHIDP-16676

How to test changes / Special notes to the reviewer

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[yangcao77]

closing this PR and reopen #351 from remote branch to trigger the CI