feat: Add a pre-chat form on widget (#1769)

app/views/api/v1/models/_widget_message.json.jbuilder

@@ -0,0 +1,9 @@
+json.id resource.id
+json.content resource.content
+json.message_type resource.message_type_before_type_cast
+json.content_type resource.content_type
+json.content_attributes resource.content_attributes
+json.created_at resource.created_at.to_i
+json.conversation_id resource.conversation.display_id
+json.attachments resource.attachments.map(&:push_event_data) if resource.attachments.present?
+json.sender resource.sender.push_event_data if resource.sender

app/views/api/v1/widget/conversations/create.json.jbuilder

@@ -0,0 +1,10 @@
+json.id @conversation.display_id
+json.inbox_id @conversation.inbox_id
+json.contact_last_seen_at @conversation.contact_last_seen_at.to_i
+json.status @conversation.status
+json.messages do
+  json.array! @conversation.messages do |message|
+    json.partial! 'api/v1/models/widget_message', resource: message
+  end
+end
+json.contact @conversation.contact