feat:check and output invalid users

[cunla]

This should:

• Ignore invalid users in the org.tfvars file.
• Output as part of the apply command the invalid users (which should be removed afterwards).

[github-actions]

Terraform plan in terraform
With var files: terraform/production/org.tfvars terraform/production/repositories.tfvars
With variables: github_token = (sensitive value)

Changes to Outputs.

Changes to Outputs:
+   invalid_users = []

You can apply this plan to save these new output values to the Terraform
state, without changing any real infrastructure.

📝 Plan generated in Plan org changes and list them in a PR #62

[tim-schilling]

Looks good to squash and merge. Thanks Daniel!