Add dropdown item for cyclonedx export

What does this MR do and why?

This MR adds a new dropdown menu item to export the dependency list in CycloneDX format.

This MR is part of a stack:

1. Add CycloneDX exporter (!185516 - merged)
2. Add cylonedx export parameter (!185517 - merged)
3. ➡️ Add dropdown item for cyclonedx export (!185518 - merged) (You are here)

References

• CycloneDX export for the project dependency list (#524733 - closed)

Screenshots or screen recordings

Before	After

Screen_Recording_2025-03-28_at_1.09.19_PM

How to set up and validate locally

1. Set up the dependency list
2. Enable the feature flag: echo 'Feature.enable(:cyclonedx_dependency_list_export)' | bundle exec rails c
3. On your project go to Security -> Dependency List
4. Click Export -> Export as CycloneDX (JSON)
5. Go to <gdk_url>/rails/letter_opener/ to download the export

MR acceptance checklist

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