raise a more informative NoMethodError for missing custom queries

the custom query container used to raise:

    NoMethodError: undefined method 'new' for nil:NilClass`

this error doesn't do much to help callers figure out where they've gone
awry. the updated message includes:

  - the originally called method name
  - the list of available methods to call (as a kind of 'did you mean' feature)
  - reference to the idea that queries need to be registered

hopefully these are all helpful reminders in dubugging.

lib/valkyrie/persistence/custom_query_container.rb

@@ -47,7 +47,11 @@ def register_query_handler(query_handler)
     end
 
     def method_missing(meth_name, *args, &block)
-      query_handler = find_query_handler(meth_name).new(query_service: query_service)
+      handler_class =
+        find_query_handler(meth_name) ||
+        raise(NoMethodError, "Custom query #{meth_name} is not registered. The registered queries are: #{queries}")
+
+      query_handler = handler_class.new(query_service: query_service)
       return super unless query_handler
       query_handler.__send__(meth_name, *args, &block)
     end
@@ -59,5 +63,11 @@ def find_query_handler(method)
     def respond_to_missing?(meth_name, _args)
       find_query_handler(meth_name).present?
     end
+
+    private
+
+    def queries
+      query_handlers.map(&:queries).flatten
+    end
   end
 end