Update environment variables with the Houston API

mutation UpdateDeploymentVariables {
  updateDeploymentVariables(
    deploymentUuid: ID! = "<deployment-id>",
  	releaseName: String! = "<deployment-release-name>",
    environmentVariables: [
      {key: "<environment-variable-1>",
      value: "<environment-variable-value-1>",
      isSecret: <true-or-false>},
      {key: "<environment-variable-2>",
      value: "<environment-variable-value-2>",
      isSecret: <true-or-false>}
    ]
  ) {
    key
    value
    isSecret
  }
}