Set node_id in github_organization data source

[douglascayers]

Summary

The github/data_source_github_organization.go defines a node_id (String) in its schema but the code doesn't actually output that value. This PR fixes that.

Changes

• Update the dataSourceGithubOrganizationRead function to set the node_id value in the generated result.
• Update unit test to check for all fields in the expected schema.
• Update documentation to describe id, node_id, and orgname properties exposed in the schema.

Usage

Example configuration:

data "github_organization" "org" {
  name = "integrations"
}

Example output:

{
  "resources": [
    {
      "mode": "data",
      "type": "github_organization",
      "name": "org",
      "instances": [
        {
          "schema_version": 0,
          "attributes": {
            "description": "Integrations built and run by GitHub. If you're looking for more GitHub integrations, see https://github.com/marketplace",
            "id": "84390928",
            "login": "integrations",
            "members": [
              "octocat",
              "kfcampbell"
            ],
            "name": "GitHub integrations",
            "node_id": "MDEyOk9yJ7FuvXpydGlpbjg2NGkwOTE3",
            "orgname": "integrations",
            "plan": "enterprise",
            "repositories": [
              "integrations/terraform-provider-github",
              "integrations/slack"
            ]
          },
          "sensitive_attributes": []
        }
      ]
    }
  ]
}

[douglascayers]

Hi @kfcampbell, would appreciate your review of this PR to populate node_id when reading organizations. Thanks!

[kfcampbell]

Thank you for updating the test and documentation as well!