docs(serverless-adapter): add another lib to benchmarks

[H4ad]

Adding my serverless-adapter lib to benchmark section.

Results:

aws-serverless-express x 12,355 ops/sec ±0.97% (85 runs sampled)
aws-serverless-fastify x 15,357 ops/sec ±0.70% (83 runs sampled)
serverless-http x 25,177 ops/sec ±2.07% (83 runs sampled)
@h4ad/serverless-adapter x 100,646 ops/sec ±0.82% (87 runs sampled)
aws-lambda-fastify x 35,063 ops/sec ±2.49% (80 runs sampled)
aws-lambda-fastify (serializeLambdaArguments : true) x 36,647 ops/sec ±0.87% (85 runs sampled)
aws-lambda-fastify (decorateRequest : false) x 36,463 ops/sec ±1.01% (85 runs sampled)
Fastest is @h4ad/serverless-adapter

I slightly modified the event object to include properties that exist on the payload that my library expect and use.

Checklist

• [x] run npm run test and npm run performance
• [x] tests and/or benchmarks are included
• [x] documentation is changed or added
• [x] commit message and code follows the Developer's Certification of Origin and the Code of conduct