Resources should support write-only attributes

[mgriffin13]

Terraform v1.11.0+ now support ephemeral resources and write-only attributes (https://github.com/hashicorp/terraform/releases/tag/v1.11.0)

Using write-only attributes will enable the use of ephemeral resources where we pull sensitive values out of Hashicorp vault to populate certain Harness resources.

My immediate use case is to populate the ssh_private_key on the https://registry.terraform.io/providers/harness/harness/latest/docs/resources/platform_gitops_repo_cred resource, but I'm sure the configuration would be useful in other places too.

For reference, you can read how HC did it, by creating a secondard _wo attribute to enable the backwards compatibility.

https://registry.terraform.io/providers/hashicorp/vault/latest/docs/guides/using_write_only_attributes