My Jetpack: Fire Tracks event when clicking CTA button on product Interstitial page

[oskosk]

Adds tracking for click on product interstitial pages CTA buttons

Changes proposed in this Pull Request:

• Introduces firing of jetpack_myjetpack_product_interstitial_add_link_click.

Jetpack product discussion

Does this pull request change what data or activity we track or use?

Introduces 1 new event:

• jetpack_myjetpack_product_interstitial_add_link_click fired when the user clicks the interstitial page add button

Testing instructions:

• Checkout this branch on a site with Jetpack connected the Backup plugin active, and the JETPACK_ENABLE_MY_JETPACK constant set to true.
• Open the browser and visit the site's wp-admin.
• Open the developer console, execute the following code: localStorage.debug='dops:analyitics*
• Go to this patch wp-admin/admin.php?page=my-jetpack#/add-boost.
• Click the Add... button
• Confirm that the developer console displays the events jetpack_myjetpack_product_interstitial_add_link_click

[github-actions]

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[retrofox]

I think the event should be named onAdd(), or something like that. If you agree, we can rename it in a follow-up PR

Suggested change

	<ProductDetail slug={ slug } trackButtonClick={ trackProductClick } />
	<ProductDetail slug={ slug } onAdd={ trackProductClick } />

[retrofox]

LGTM