fix: Add extraEnv option to Helm chart

[gnadaban]

Description

This is a small fix to account for the lack of ability to add extra env vars to the trivy-operator deployment. This allows specifying eg. AWS IAM session names and other options for eg. secret injection.

Related issues

• Close #2287

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Checklist

• [x] 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.
• [x] 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).