No drift detection for GitHub config

[AgaDufrat]

Old GitHub configuration script used to run daily overwriting any manual changes. The new implementation with Terraform needs to be manually applied.

We may want to consider:

• having some drift detection and notifications.
  • https://app.terraform.io/app/govuk/workspaces/GitHub/health/drift
  • https://developer.hashicorp.com/terraform/cloud-docs/workspaces/settings/notifications
  • https://registry.terraform.io/providers/hashicorp/tfe/latest/docs/resources/notification_configuration
• (not advised) consider a scheduled plan/apply. This can be done via API https://developer.hashicorp.com/terraform/cloud-docs/api-docs/run#create-a-run