feat: new premium upsell button style

[braindigitalis]

Adds the premium upsell button: https://discord.com/developers/docs/change-log#premium-apps-new-premium-button-style-deep-linking-url-schemes

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• [x] I have ensured that all methods and functions are fully documented using doxygen style comments.
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• [x] I tested that my change works before raising the PR.
• [x] I have ensured that I did not break any existing API calls.
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