Show disabled button state when missing required fields

[JorgeMucientes]

Closes: WOOMOB-940

Description

The current support form is a bit confusing because the "Submit Support Request" is shown as enabled even when it is disabled behind scenes because there's missing required info in the form.
This PR simply adds a disabled state to the button so that it reflects it's current enabled/disabled status clearly

Steps to reproduce

Testing information

1. Navigate to Settings > Help & Support > Contact Support
2. Verify the button is shown as disabled in both light and dark mode
3. Enter all the required field
4. Check how the button is shown as enabled
5. Erase any of the required fields and confirm the button is shown as disabled again.

The tests that have been performed

The above

Screen_recording_20250822_103530.mp4

[wpmobilebot]

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

	App Name	WooCommerce Android
	Platform	📱 Mobile
	Flavor	Jalapeno
	Build Type	Debug
	Commit	5e58072
	Direct Download	woocommerce-prototype-build-pr14507-5e58072.apk

[wpmobilebot]

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

	App Name	WooCommerce-Wear Android
	Platform	⌚️ Wear OS
	Flavor	Jalapeno
	Build Type	Debug
	Commit	5e58072
	Direct Download	woocommerce-wear-prototype-build-pr14507-5e58072.apk

[irfano]

LGTM! 👍🏻