Adding selectmenus to modals

[Ekcum]

Discord introduced today selectmenus in modals.

I would be happy to add the functionality to serenity if nobody else is interested or doesnt have time to do so. :D

[JakobLachermeier]

I've been looking into what it would take to implement this.

Right now, serenity uses ActionRows for modal items, which seem to be deprecated and don't support String Selects.

This means CreateModal.components() would have to be changed from accepting Vec<CreateActionRow> to Vec<CreateLabel>.
CreateLabel would need to be newly added and serialize like this.

Before I start, I'd like some guidance on whether this should be done in the next or current branch, and if changing the existing CreateModal component is acceptable.

To keep current working with CreateActionRow, those action rows could be converted to CreateLabel inside CreateModal to hide the change from the user and maintain a compatible user-facing API.

[KiloOscarSix]

I've begun working on this on the next branch with breaking changes (like changing CreateModal).
Draft PR will be available later today once I'm back at my desktop to ensure the PR follows the contributing guidelines.

[mkrasnitski]

This work is already in progress in #3430. And, while Action Rows in modals are deprecated, they have not been disallowed yet. You can verify this by providing an unsupported top-level component in a modal, and the error message from the API will mention only top-level components of type 1 (Action Row), 10 (Text Display), or 18 (Label) are allowed.

[KiloOscarSix]

Ah cheers, missed that PR