fix: add user-agent headers to requests with pypiclient

[JamieMagee]

This will add 2 User-Agent headers to all requests to PyPI:

• ComponentDetection/{version} (A product identifier)
• (+https://github.com/microsoft/component-detection) (A comment)

See MDN documentation for more details on this header: https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/User-Agent

[github-actions]

👋 Hi! It looks like you modified some files in the Detectors folder.
You may need to bump the detector versions if any of the following scenarios apply:

• The detector detects more or fewer components than before
• The detector generates different parent/child graph relationships than before
• The detector generates different devDependencies values than before

If none of the above scenarios apply, feel free to ignore this comment 🙂