core: Add support for marking outputs as sensitive (#6559)
core: Add support for marking outputs as sensitive (#6559)

* core: Add support for marking outputs as sensitive

This commit allows an output to be marked "sensitive", in which case the
value is redacted in the post-refresh and post-apply list of outputs.

For example, the configuration:

```
variable "input" {
    default = "Hello world"
}

output "notsensitive" {
    value = "${var.input}"
}

output "sensitive" {
    sensitive = true
    value = "${var.input}"
}
```

Would result in the output:

```
terraform apply

Apply complete! Resources: 0 added, 0 changed, 0 destroyed.

Outputs:

  notsensitive = Hello world
  sensitive    = <sensitive>
```

The `terraform output` command continues to display the value as before.

Limitations: Note that sensitivity is not tracked internally, so if the
output is interpolated in another module into a resource, the value will
be displayed. The value is still present in the state.
hashicorp/terraform-plugin-sdk,hashicorp/terraform-plugin-sdk