docs: Enhance example of using waitForTaskToken to show both state machine and lambda

[dmeehan1968]

Here is an expanded example for waitForTaskToken, using a lambda as the worker. It simply waits for the specified time or timestamp, then sends the final status to resume the calling state machine.

export const main = asl.deploy.asStateMachine(async (input: any, context: asl.StateMachineContext<any>) => {

    const result = await asl.task<WorkerOutput>({
        resource: 'arn:aws:states:::lambda:invoke.waitForTaskToken',
        parameters: {
            FunctionName: asl.deploy.getLambdaName('workerTask'),
            Payload: {
                seconds: 5,
                taskToken: context.task.token,
            }
        },
        retry: [
            {
                errorEquals: ['States.ALL'],
                maxAttempts: 0,
            },
        ],
        timeoutSeconds: 10,
        heartbeatSeconds: 10,
    })
})

interface WorkerOutput {
    status: 'completed' | 'failed'
}

interface RelativeWait {
    seconds: number
    timestamp?: undefined
}

interface AbsoluteWait {
    seconds?: undefined
    timestamp: string
}

// discriminated union to switch between relative or absolute delays
type WaitInput = (RelativeWait | AbsoluteWait) & { taskToken: string }

export const workerTask = asl.deploy.asLambda(async (input: WaitInput) => {
    if (input.seconds) {
        await new Promise((resolve) => setTimeout(resolve, input.seconds * 1000))
    } else if (input.timestamp) {
        const timeout = Math.max(new Date(input.timestamp).getTime() - Date.now(), 0)
        await new Promise((resolve) => setTimeout(resolve, timeout))
    } else {
        console.error('waitTask: no seconds or timestamp provided')
        await asl.sdk(SFN).sendTaskFailure({
            parameters: {
                error: JSON.stringify({ status: 'failed' }),
                taskToken: input.taskToken,
            }
        })
    }

    await asl.sdk(SFN).sendTaskSuccess({
        parameters: {
            taskToken: input.taskToken,
            output: JSON.stringify({ status: 'completed' }),
        }
    })

    console.log('completed waitTask')
})