Introduce Error Enum to node-fetch

[lautarodragan]

Creating this issue to track the work done, even though part of the work will be done in another repo.

https://github.com/poetapp/node/blob/7b675984d116d907847e7bb5f119cbae8ae99d97/src/Helpers/FetchError.ts#L3-L13

Will also need to delete the enum from our code base and import node-fetch's one if the PR gets accepted and published.

Will try and tackle this one next Friday, as it's not immediately critical to our progress but something I'd like to see.