feat(helm): change extraEnv to map with envFrom, add extraEnvSecrets

[rzala]

• [BREAKING] Change extraEnv from a list (inline env vars) to a map rendered into a ConfigMap and attached via envFrom
• Add extraEnvSecrets map rendered into a Secret (stringData) via envFrom
• Simpler key/value format replaces verbose name/value list syntax

Checklist

• I've read the guidelines for contributing to this repository.
• I've added tests that prove my fix is effective or that my feature works.
• I've updated the documentation with the relevant information (if needed).
• I've added usage information (if the PR introduces new options)
• I've included a "before" and "after" example to the description (if the PR is a user interface change).