[HACK] AI API keys: Settings view

[iamgabrielma]

HACK week. Part of #15372

Description

This PR adds the dummy Settings view where the merchant can introduce their API key, and select provider/model, or be informed that their site is already using built-in AI.

Testing information

• Enable allowMerchantAIAPIKey flag
• Go to Menu > AI Settings.
• Note the new view has fields for key, provider, and model that can be toggled. This is non-functional yet, just the UI.
• Switch usesJetpackAsDefaultAIProviderSource to true
• Note the new view shows a disclaimer instead that is already using built-in AI, and the fields are locked/disabled

Merchant key	Jetpack key

[wpmobilebot]

📲 You can test the changes from this Pull Request in WooCommerce iOS Prototype by scanning the QR code below to install the corresponding build.

	App Name	WooCommerce iOS Prototype
	Build Number	pr16135-a3ac5bf
	Version	23.2
	Bundle ID	com.automattic.alpha.woocommerce
	Commit	a3ac5bf
	Installation URL	14567pid8l980

Automatticians: You can use our internal self-serve MC tool to give yourself access to those builds if needed.

[iamgabrielma]

Closing: pdfdoF-85K#comment-9421-p2