Add duo_add_otel feature flag & ProjectsHelper#show_duo_otel_button?

What does this MR do and why?

Add a feature flag and a method to the ProjectsHelper that will be used to determine whether or not to show a button to generate an issue for instrumenting OpenTelemetry and kicking off a duo workflow.

Duo generated summary

This change adds a new feature called "duo_add_otel" that's currently disabled by default and in work-in-progress status. The main addition is a function that determines whether to show a special "Duo OTEL" button to users based on several conditions: the project must have code in it, contain programming languages, the user must have permission to modify code, and various AI-related features must be enabled for the project. The change also includes comprehensive tests to verify the button only appears when all these requirements are met, and stays hidden when any condition fails.

References

Add a button to the project page that instruments OpenTelemetry

Screenshots or screen recordings

No UI changes

How to set up and validate locally

The specs should cover all validation

MR acceptance checklist

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