feat(secrets-management): add cloud-kms references for aws and gcp

[rawkode]

Summary

• add cloud-kms reference docs under secrets-management
• add AWS reference with AWS KMS + Secrets Manager + ESO manifests and Terraform
• add GCP reference with Cloud KMS + Secret Manager + ESO manifests and Terraform
• automate CKS OIDC issuer wiring via Terraform by reading cks_service_account_oidc_issuer_url from CKS terraform remote state
• add optional automation for AWS OIDC provider creation and GCP WIF pool/provider creation

Validation

• terraform fmt checks passed for AWS and GCP Terraform directories
• terraform validate is blocked in this environment by Terraform/provider runtime compatibility for installed provider plugins
• runtime manifest validation requires connected cluster auth