No replacement for the @LambdaFunction and LambdaInvokerFactory?

## Expected Behavior

One of the great API improvements provided by the v1 SDK was the [LambdaInvokerFactory](https://docs.aws.amazon.com/AWSJavaSDK/latest/javadoc/com/amazonaws/services/lambda/invoke/LambdaInvokerFactory.html), which handled so much of the marshalling when directly invoking a Lambda.

There seems to be no v2 replacement that I can find, and nothing is mentioned in the [1.11 to 2.0 changelog](https://github.com/aws/aws-sdk-java-v2/blob/master/docs/LaunchChangelog.md) which is surprising for something that completely disappeared.

## Current Behavior

There is no corollary to the `@LambdaFunction` and `LambdaInvokerFactory` set of API utilities.

## Possible Solution

Re-implement those utilities.

## Context

The amount of boilerplate *significantly* increases when attempting to call Lambda. This is especially apparent when writing functional tests, where the actual details of invoking a Lambda are not relevant to actually testing that Lambda.

## Your Environment

* AWS Java SDK version used: v2
* JDK version used: Corretto - 11.0.8
* Operating System and version: Ubuntu 20.04