refactor(rpm): Moved openshell-gateway.service from RPM to dedicated file

[engelmi]

Summary

The inline heredocs in the openshell.spec is hard to lint, diff, and edit. Therefore, moving it into a dedicated file so it gets proper syntax highlighting, can be validated by systemd-analyze verify and is easier to review in isolation.
This also aligns with the .deb packaging.

Related Issue

No issue required: Small, mechanical change

Changes

Moves the RPM packaged openshell-gateway.service from spec file to deploy/rpm/openshell-gateway.service

Testing

• mise run pre-commit passes
• Unit tests added/updated (not needed)
• E2E tests added/updated (if applicable)

Checklist

• Follows Conventional Commits
• Commits are signed off (DCO)
• Architecture docs updated (if applicable)

[copy-pr-bot]

This pull request requires additional validation before any workflows can run on NVIDIA's runners.

Pull request vetters can view their responsibilities here.

Contributors can view more details about this message here.

[github-actions]

All contributors have signed the DCO ✍️ ✅
_{Posted by the DCO Assistant Lite bot.}

[engelmi]

I have read the DCO document and I hereby sign the DCO.

[engelmi]

Rebased the branch with the latest changes on main

[engelmi]

/ok to test

[engelmi]

@mrunalp Could you trigger the pending (required) CI runs? It seems I lack the necessary privileges.

[mrunalp]

/ok to test d572852

[engelmi]

Anything blocking this from being merged? Its just a small change and approved.

[engelmi]

@mrunalp Could this be merged?

[github-actions]

This pull request has had no activity for 14 days and is now marked stale. It may be closed in 7 days if there is no further activity.

[politerealism]

@mrunalp this one's been sitting since early August with an approved CI run and a dismissed review (looks like just from a later commit, not a rejection). it's a small, mechanical move with no functional change, and the stale-bot is about to close it. Could you take another look or point to who can merge it?

[engelmi]

@mrunalp @derekwaynecarr I had to rebase. Could you trigger the CI again?