Add first_name and last_name field to the Siteglide API CRM endpoint

Linked to Forum discussion: https://forum.siteglide.com/post/adding-contacts-from-siteglide-forms-through-zapier-to-mailchimp-5f0a37710f73d33ae127d789?post=5f0d70cad2e356203e447b29

This will be useful in some integrations e.g. Mailchimp