Double-encoded attributes: need feature that will allow us to transform sensitive data from Terraform state before being stored in a connection details secret

### What problem are you facing?

During investigating bug for the double-encoded attributes https://github.com/upbound/provider-azure/issues/276 founded that we need feature that will allow us to transform sensitive data from Terraform state before being stored in a connection details secret ( to avoid using a workaround - AdditionalConnectionDetailsFn configuration.)

Problem azure resource: azurerm_kubernetes_cluster - attribute.kube_config.0.client_certificate, attribute.kube_config.0.client_key, attribute.kube_config.0.cluster_ca_certificate - this attributes are encoded twice

### How could Upjet help solve your problem?

Implementation feature that will allow us to transform sensitive data from Terraform state before being stored in a connection details secret.