The `PromptElement` data type cannot be unknown

[aaroncox]

session/src/ui.ts

Lines 19 to 23 in 20d64d6

	export interface PromptElement {
	type: 'accept' | 'asset' | 'button' | 'close' | 'countdown' | 'link' | 'qr' | 'textarea'
	label?: string
	data?: unknown
	}

While writing documentation I noticed that data: unknown still exists in the code. This needs to be more well defined and create constraints for the various types of elements that can be used, otherwise the instances of the UserInterface (like the @wharfkit/web-renderer) can just accept whatever data they want. This data needs to be standardized so that every implementation of the UserInterface has to follow the same rules.

It was good that this was unknown during development, while we still defined how interactivity occurred, but now needs to change over.

Related slack thread: https://greymass.slack.com/archives/C045MUS6F0F/p1685569547180519