Graphql / Uplift user data source

[patrickmarabeas]

Uplifts the user data source to use v4 API

API surface has been reduced considerably to only return relevant data in the context of Terraform. Happy to hear opinions on this.

Example output:

user = {
  "email" = ""
  "id" = "MDQ6VXNlcjMyOTMxNDQ="
  "is_site_admin" = false
  "login" = "patrickmarabeas"
  "name" = "Patrick Marabeas"
}

notes:

• This branch will be rebased as necessary
• Shared consts and functions will be abstracted int util_* files as required, I've simply included them within the one file for simplicity for the time being
• This constitutes a preliminary migration to the v4 API
• Tests will be written / updated once the API surface is nailed down