Helm: make webapp container port configurable

[kolorful]

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What

Fix #25188

How

Update helm chart to make the HTTP port of WebApp configurable.

Recommended reading order

1. values.yaml
2. deployment.yaml

Can this PR be safely reverted / rolled back?

• [x] YES 💚
• [ ] NO ❌

🚨 User Impact 🚨

Are there any breaking changes? What is the end result perceived by the user? If yes, please merge this PR with the 🚨🚨 emoji so changelog authors can further highlight this if needed.

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