chore: Add content type enum to request (#754)

* added content type to request

Author: sbansla

src/main/java/com/twilio/http/Request.java

@@ -1,5 +1,7 @@
 package com.twilio.http;
 
+
+import com.twilio.constant.EnumConstants.ContentType;
 import com.twilio.exception.ApiException;
 import com.twilio.exception.InvalidRequestException;
 
@@ -37,6 +39,8 @@ public class Request {
 
     private List<String> userAgentExtensions;
 
+    private ContentType contentType;
+
     /**
      * Create a new API request.
      *
@@ -113,6 +117,14 @@ public List<String> getUserAgentExtensions() {
         return this.userAgentExtensions;
     }
 
+    public ContentType getContentType() {
+        return contentType;
+    }
+
+    public void setContentType(ContentType contentType) {
+        this.contentType = contentType;
+    }
+
     /**
      * Create auth string from username and password.
      *