Change Part constructor as package-scoped

Author: piotrooo

components/abstractions/src/main/java/com/microsoft/kiota/MultipartBody.java

@@ -176,7 +176,7 @@ private class Part {
         private final String contentType;
         private final String filename;
 
-        private Part(String name, Object value, String contentType, String filename) {
+        Part(String name, Object value, String contentType, String filename) {
             this.name = name;
             this.value = value;
             this.contentType = contentType;