Update gke.md service type

[Norlock]

This took me way too long to figure out, something has got to be done about documentation errors and keeping things up to date. Anyway this fix makes sure the service is properly exposed.

Type of change:

• [x] Bugfix
• [ ] New feature provided
• [ ] Improve performance
• [ ] Backport patches
• [ ] Documentation
• [ ] Refactor
• [ ] Chore
• [ ] CI/CD or Tests

What this PR does / why we need it:

The port otherwise doesn't get exposed.

[zll600]

@Revolyssup Can you merge this now?

[github-actions[bot]]

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