Add GPG and SSH key to GitHub user data source

[hashibot]

This issue was originally opened by @mootpt as hashicorp/terraform#15211. It was migrated here as part of the provider split. The original body of the issue is below.

---

Add GPG and SSH key to GitHub user data source:

data "github_user" "mootpt" {
  username = "mootpt"
}

output "mootpt-gpg" {
  value = "${data.github_user.mootpt.gpg_key}"
}

output "mootpt-ssh" {
  value = "${data.github_user.mootpt.ssh_key}"
}

[grv87]

Duplicate of #4

[stack72]

Closed via #2