feat(prefect-server): add appProtocol to service port

[lostkamp]

Summary

This is an optional field that sometimes enables additional capabilities by addons like Istio.

Docs: https://kubernetes.io/docs/concepts/services-networking/service/#application-protocol

I tried to make the usage optional in the template, not sure if this is correct actually.

Requirements

• Contributing guide has been read
• Title follows the conventional commits format
• Body includes Closes <issue>, if available
• Added/modified configuration includes a descriptive comment for documentation generation
• Unit tests are added/updated
• Deprecation/removal checks are added in templates/NOTES.txt
• Relevant labels are added
• Draft status is used until ready for review

[mitchnielsen]

Thanks for the contribution! A couple of things before we can merge:

1. The default in values.yaml should probably be "" (empty) rather than "http", so existing deployments aren't affected on upgrade.
2. Could you add a unit test covering both the set and unset cases? You can look at existing tests in charts/prefect-server/tests/ for examples.
3. Let's add a default to the schema entry to keep it in sync with values.yaml.

[mitchnielsen]

Left a comment requesting small changes 👍🏼