Add support for Lambda Response Streaming

[normj]

Issue #, if available:
#1635

Description of changes:
Integrate Lambda response streaming support into the Amazon.Lambda.RuntimeSupport.

A hello world example of using response streaming. In this case sense I wrapped the Stream returned from CreateStream in a StreamWriter the writes will be buffered in StreamWriter till the buffer is full. I call the flush method every 10 iterations to force sending data back to the client.

using Amazon.Lambda.Core;
using Amazon.Lambda.Core.ResponseStreaming;
using Amazon.Lambda.RuntimeSupport;
using Amazon.Lambda.Serialization.SystemTextJson;

#pragma warning disable CA2252

// The function handler that will be called for each Lambda event
var handler = async (string input, ILambdaContext context) =>
{
    using var responseStream = LambdaResponseStreamFactory.CreateStream();

    using var writer = new StreamWriter(responseStream);
    for (var i = 1; i <= 100; i++)
    {
        var message = $"Hello {input} - {i}";
        await writer.WriteLineAsync(message);

        if (i % 10 == 0)
        {
            await writer.FlushAsync();
            await Task.Delay(1000);
        }
    }
};

// Build the Lambda runtime client passing in the handler to call for each
// event and the JSON serializer to use for translating Lambda JSON documents
// to .NET types.
await LambdaBootstrapBuilder.Create(handler, new DefaultLambdaJsonSerializer())
        .Build()
        .RunAsync();

For a use with API Gateway or Lambda Function URL you need to create the stream with the CreateHttpStream passing the status code and response headers.

using Amazon.Lambda.APIGatewayEvents;
using Amazon.Lambda.Core;
using Amazon.Lambda.Core.ResponseStreaming;
using Amazon.Lambda.RuntimeSupport;
using Amazon.Lambda.Serialization.SystemTextJson;
using System.Net;

#pragma warning disable CA2252

// The function handler that will be called for each Lambda event
var handler = async (APIGatewayProxyRequest request, ILambdaContext context) =>
{
    var prelude = new HttpResponseStreamPrelude
    {
        StatusCode = HttpStatusCode.OK,
        Headers =
        {
            { "Content-Type", "text/plain" }
        }
    };
   
    using var responseStream = LambdaResponseStreamFactory.CreateHttpStream(prelude);

    using var writer = new StreamWriter(responseStream);
    for (var i = 1; i <= 10000000; i++)
    {
        var message = $"Hello - {i} ({responseStream.Length.ToString("N0")}) (Remaining Time: {context.RemainingTime})";
        await writer.WriteLineAsync(message);

        if (i % 100 == 0)
        {
            await writer.FlushAsync();
        }

        if (context.RemainingTime < TimeSpan.FromSeconds(5))
        {
            await writer.WriteLineAsync("Approaching Lambda timeout, stopping the stream.");
            await writer.FlushAsync();
            break;
        }
    }
};

// Build the Lambda runtime client passing in the handler to call for each
// event and the JSON serializer to use for translating Lambda JSON documents
// to .NET types.
await LambdaBootstrapBuilder.Create(handler, new DefaultLambdaJsonSerializer())
        .Build()
        .RunAsync();

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.