feat: dpp::application is now updated, added set_iconhash_not_null

[Jaskowicz1]

This PR now updates dpp::application, making it up-to-date (and even have content discord doesn't document yet). It also adds set_iconhash_not_null, meaning we don't have to do workarounds to set the iconhash as it can be set from a string.

Code change checklist

• I have ensured that all methods and functions are fully documented using doxygen style comments.
• My code follows the coding style guide.
• I tested that my change works before raising the PR.
• I have ensured that I did not break any existing API calls.
• I have not built my pull request using AI, a static analysis tool or similar without any human oversight.

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[Jaskowicz1]

Some of the new data I have added seems to maybe be in relation to this update, adding premium subscriptions in the US. However, the data is still undocumented and that update doesn't say anything about that data at all.