Loops destination: ability to sync contact properties when sending events

[danrowden]

This PR adds the ability to sync contact properties/information when sending events to Loops using a new "Contact Properties" field. This mimics the behaviour already present in the "Create or update contact" action.

Testing

• [x] Added unit tests for new functionality
• [x] Tested end-to-end using the local server
• [x] [If destination is already live] Tested for backward compatibility of destination. Note: New required fields are a breaking change.
• [ ] [Segmenters] Tested in the staging environment
• [ ] [Segmenters] [If applicable for this change] Tested for regression with Hadron.