Add supports to GoogleAnalytics BeginCheckoutEvent

[Scarbous]

implement supports function for BeginCheckoutEvent like ViewItemListEvent

1. Why is this change necessary?

• Prevent errors, when the "begin-checkout-btn" gets removed from the CartOverlay.

2. What does this change do, exactly?

• Only trigger the event if the "begin-checkout-btn" exists

3. Describe each step to reproduce the issue or behaviour.

• Remove "begin-checkout-btn" from CarOverlay template
• Add Item to cart
• Open Cart Overlay
• Marvel at the exception 🙃

4. Please link to the relevant issues (if any).

5. Checklist

• [x] I have rebased my changes to remove merge conflicts
• [ ] I have written tests and verified that they fail without my change
• [ ] I have created a changelog file with all necessary information about my changes
• [ ] I have written or adjusted the documentation according to my changes
• [ ] This change has comments for package types, values, functions, and non-obvious lines of code
• [ ] I have read the contribution requirements and fulfil them.

[github-actions[bot]]

	Warnings
:warning:	The Pull Request doesn't contain any changelog file