SmartCollection Metafields

[shawnhind]

With the SDK it's currently not possible to add metafields to SmartCollections (from what I can see).

According to this doc page:
https://help.shopify.com/en/api/reference/metafield

It should be possible to add metafields to SmartCollections using the /collections/{id}/metafields.json endpoint. I've tested using postman and it is indeed possible to add metafields to those objects using the collections resource but I couldn't figure out how to do this with the SDK. I'm currently using a manual HTTP request to do this call instead.

[tompec]

@shawnhind I just PR'd a fix to this #43

[tareqtms]

Fixed with #43