add labels required by istio

[PatTheSilent]

• Breaking change? (if so, please describe the impact and migration path for existing application instances)

What changes did you make? (Give an overview)
I've added labels required by istio.
Without these labels istio reports traffic coming from kafka-ui to kafka connect and schema registry with a label source_app set to unknown, which is far from ideal. Visualizations tools like kiali or Grafana dashboards rely on the source_app label in istio metrics to present traffic flowing through environments.

Oh, and apparently my IDE has corrected some whitespaces. I can remove those if they don't meet your conventions or you don't want them.

Is there anything you'd like reviewers to focus on?

Their happiness and wellbeing.

How Has This Been Tested? (put an "x" (case-sensitive!) next to an item)

• No need to
• Manually (please, describe, if necessary)
• Unit checks
• Integration checks
• Covered by existing automation

Checklist (put an "x" (case-sensitive!) next to all the items, otherwise the build will fail)

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation (e.g. ENVIRONMENT VARIABLES)
• My changes generate no new warnings (e.g. Sonar is happy)
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged

Check out Contributing and Code of Conduct

A picture of a cute animal (not mandatory but encouraged)
Adding a cute corgi

[github-actions]

Hello there PatTheSilent! 👋

Thank you and congrats 🎉 for opening your first PR on this project! ✨ 💖

We will try to review it soon!

[Haarolean]

Hey, thanks for the contribution. We'll take a look :)

[azatsafin]

Do not see any breacking changes, we could merge it

[Haarolean]

@PatTheSilent thank you!