[Part 1 ] Add cart abandonment endpoint to hand raise leads controller

What does this MR do and why?

This MR adds tracking endpoint for upgrade button clicks on the group billing page to support cart abandonment email functionality.

When users click the "Upgrade to Premium" or "Upgrade to Ultimate" buttons on the billing page, we now track this interaction before navigating them to the customers portal. This tracking will enable us to identify users who show purchase intent but don't complete the transaction, allowing us to send targeted re-engagement emails.

• Adds a track_cart_abandonmentend point to capture upgrade button clicks
• Adds tracking URL parameters to the billing page data attributes
• Includes authorization checks (owner-only access)

The tracking logic implementation will be added in a follow-up MR.

References

#577574

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There are no UI changes

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Related to #577574