feat: allow aggregate ordering of through table edges

[michaelcaulley]

Summary

• Add support for using entgql.OrderField() aggregates for edges that use a Through table.
• The OrderField string must be prefixed with the string value of the edge. For example:

	edge.To("friends", User.Type).
			Through("friendships", Friendship.Type).
			Annotations(entgql.RelayConnection()),

would require the OrderField string to start with FRIENDS_

For the count aggregation the full string would be FRIENDS_COUNT.

• The changes skip the through table OrderBy and only use the original edge OrderBy.