[terraform-ibm-observability-da] Scope KMS COS auth policies to KMS key

[ocofaigh]

• Once Updated the KMS auth policy so its scoped to the exact KMS Key terraform-ibm-cos#764 is merged pull in the new version to the DA. That will ensure any KMS policy created in that module will be scoped to the key.
• Update the cross account auth policy created in the DA directly to scope to the exact KMS key