[Blaze] Suggest CTA text using AI

[hichamboushaba]

Closes: #14376

Description

This PR updates the Blaze suggestion API to include the cta_text field, and use it in the campaign creation flow.

Steps to reproduce

1. Use a blaze eligible website.
2. Open the app.
3. Start blaze campaign creation.

Testing information

• Confirm that the CTA text is pre-filled like tagline and description.
• Edit the ad and confirm you can select different versions of the CTA text.
• Make manual changes, and confirm they work without issues.

Screenshots

https://github.com/user-attachments/assets/7c1936d2-b078-41a2-be86-c42f655f27fd

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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.

Reviewer (or Author, in the case of optional code reviews):

Please make sure these conditions are met before approving the PR, or request changes if the PR needs improvement:

• [x] The PR is small and has a clear, single focus, or a valid explanation is provided in the description. If needed, please request to split it into smaller PRs.
• [x] Ensure Adequate Unit Test Coverage: The changes are reasonably covered by unit tests or an explanation is provided in the PR description.
• [x] Manual Testing: The author listed all the tests they ran, including smoke tests when needed (e.g., for refactorings). The reviewer confirmed that the PR works as expected on all devices (phone/tablet) and no regressions are added.

[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	pr14399-6c613ab
	Version	21.1
	Bundle ID	com.automattic.alpha.woocommerce
	Commit	6c613abf29708c67b4fd734a5693d055e1b59c56
	App Center Build	WooCommerce - Prototype Builds #11596

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