Support dynamically configuring the JDG protobuf schema

Need to add the ability to dynamically configure the protobuf schema. A
snip-it from an example:

// generate and register a Protobuf schema and marshallers based on Note class and the referenced classes (User class)
ProtoSchemaBuilder protoSchemaBuilder = new ProtoSchemaBuilder();
String generatedSchema = protoSchemaBuilder
.fileName("sample_schema.proto")
.packageName("sample_package")
.addClass(Note.class)
.build(serCtx);

This would change the need for the user to implement marshallers.