chore(helm): upgrade bundled Redis from 7.0.15 to 7.4.9 (#41792)

## Summary
- Bumps the default Redis image tag in the Helm chart from `7.0.15` to
`7.4.9` to address accumulated CVEs in the 7.0.x line
- Also updates the example comment in the `initContainer` section to
match

## Test plan
- [x] Test on non-prod deployments and verify cluster status

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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## Summary by CodeRabbit

* **Chores**
  * Updated Redis dependency to version 7.4.9.

[![Review Change
Stack](https://storage.googleapis.com/coderabbit_public_assets/review-stack-in-coderabbit-ui.svg)](https://app.coderabbit.ai/change-stack/appsmithorg/appsmith/pull/41792)

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<!-- This is an auto-generated comment: Cypress test results  -->
> [!WARNING]
> Tests have not run on the HEAD
1cf4fdbf76f9d082a5a31f7e22b3f39609f9175f yet
> <hr>Mon, 11 May 2026 18:40:36 UTC
<!-- end of auto-generated comment: Cypress test results  -->

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Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>