Feature: Create better support for custom connections

[cshadek]

There was discussion in #106 about enabling better support for custom connections and recent changes were made to make that easier to implement in #107, #108, and #109.

1. Ideally it would be nice to have an easy way to declare connections with custom fields and edges with custom fields. I'm not exactly sure the best way to implement this, but it would be nice to have the customization and at the same time utilize the existing connection code, including slicing, etc.

@NeedleInAJayStack I know you mentioned you had begun to think about how this might be accomplished.

2. In addition, maybe it makes sense to also think about the "connection of a protocol" issue where because Node needs to implement Encodable, it is currently not possible to have a connection of a Union or Interface. There is a fix, and that is to create a wrapper type, but that's obviously not the cleanest approach.

A possible solution to 2 was mentioned here: https://github.com/GraphQLSwift/Graphiti/issues/50#issuecomment-776896528

[NeedleInAJayStack]

Just put in a pull request that addresses item 1: https://github.com/GraphQLSwift/Graphiti/pull/112

[cshadek]

Well that was fast!