#3848930 composite-checkout: Add error boundary around top level (1)

Changes proposed in this Pull Request

This adds a React error boundary around the entire component tree of composite checkout starting at CheckoutSystemDecider. Hopefully this will never be hit because composite checkout already has several layers of error boundaries within CheckoutProvider but it will give us the opportunity to:

1. Prevent the user from seeing a blank screen if something at the top level fails.
2. Record such errors and report them to logstash where they will ping us in Slack.

Testing instructions

• Trigger a fatal error inside the CompositeCheckout component itself.
• Verify that the logstash logs for the string composite checkout load error get a new entry.