Add CS_TRIVY_TIMEOUT Environment Variable

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This MR adds a CS_TRIVY_TIMEOUT environment variable to set a custom trivy timeout for scanning large images. This is a feature in trivy image but is currently unavailable as a configuration flag in the gitlab container scanning product.

What are the relevant issue numbers?

gitlab-org/gitlab#450298

Does this MR meet the acceptance criteria?

• Changelog entry added
• Documentation created/updated for GitLab EE, if necessary - gitlab-org/gitlab!150550 (closed)
• Documentation created/updated for this project, if necessary
• Documentation reviewed by technical writer or follow-up review issue created
• Tests added for this feature/bug
• Job definition updated, if necessary
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• Conforms to the code review guidelines
• Conforms to the Go guidelines
• Security reports checked/validated by reviewer