`databricks_cluster_policy` should use `library` blocks for consistency

[nkvuong]

          the issue is with the user code - this is how you specify multiple libraries.

@edwardfeng-db normally, we need to alias plural to singular, i.e. library to avoid confusion for users. Especially as clusters & jobs use singular library

resource "databricks_cluster_policy" "fair_use" {
  name       = "test cluster policy"
  definition = jsonencode(local.default_policy)

  libraries {
    maven {
      coordinates = "com.oracle.database.jdbc:ojdbc8:XXXX"
    }
  }
  libraries {
    pypi {
      package = "databricks-sdk==0.12.0"
    }
  }
}

Originally posted by @nkvuong in https://github.com/databricks/terraform-provider-databricks/issues/3612#issuecomment-2190015096