feat(test-utils): add option to configure test server port

[gjedlicska]

🔗 Linked issue

#20442

❓ Type of change

• 📖 Documentation (updates to the documentation, readme or JSdoc annotations)
• 🐞 Bug fix (a non-breaking change that fixes an issue)
• 👌 Enhancement (improving an existing functionality like performance)
• ✨ New feature (a non-breaking change that adds functionality)
• 🧹 Chore (updates to the build process or auxiliary tools and libraries)
• ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

This PR adds an optional port value to the test-utils TestOptions interface.

This value enables pinning the test server's port when calling the setup function.

The feature is required for some integration test purposes, when the tested nuxt based server backend is expected to receive a callback from the service its being tested against. Without knowing the test server's port in advance, its a lot harder to configure these sorts of tests.

Resolves #20442

📝 Checklist

• I have linked an issue or discussion.
• I have updated the documentation accordingly.

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[fabis94]

Yes please!