Dynamic Dashboard: Save and load last selected stock type for Stock card

[itsmeichigo]

Closes: #12797
Part of #12754

Description

This PR updates AppSettingsStore and AppSettingsAction to support saving and loading last selected stock type for Stock card.

ProductStockDashboardCardViewModel has also been updated to load the last selected stock type upon initialization and set the selected stock type when it changes.

Testing instructions

• Log in to a store and enable the Stock card on My Store.
• Confirm that the initial selected stock type is Low stock.
• Switch to a different stock type.
• Relaunch the app, confirm that the last selected stock type is displayed instead of low stock.

Screenshots

N/A

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• I have considered if this change warrants user-facing release notes and have added them to RELEASE-NOTES.txt if necessary.

[wpmobilebot]

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

	App Name	WooCommerce iOS
	Build Number	pr12800-ad7fdf1
	Version	18.7
	Bundle ID	com.automattic.alpha.woocommerce
	Commit	ad7fdf1
	App Center Build	WooCommerce - Prototype Builds #9171

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

[selanthiraiyan]

🚀