Maintenance: Improve example documentation

[scottgerring]

Summary

Apart from powertools-core, the example documentation READMEs miss usage instructions beyond "deploy with SAM".

Why is this needed?

This makes it hard to use the examples. For instance, in the case of the idempotency demo, a particular JSON body needs to be POSTed to the API created, which is not obvious. This friction reduces the value of the

Which area does this relate to?

Other

Solution

Improve the documentation of the following examples to describe 1/ how to use them and 2/ what they are doing and why.

• idempotency
• parameters
• deserialization
• batch processing

While we are at it, let's go through the code itself and make sure it is up to date and clear.

Finally, the main powertools documentation should be updated to link to the relevant demos for each piece of code.

Acknowledgment

• This request meets Powertools for AWS Lambda (Java) Tenets
• Should this be considered in other Powertools for AWS Lambda (Java) languages? i.e. Python, TypeScript

[scottgerring]

For the powertools-idempotency example, the user must POST a JSON object in the following format:

{
	"address": "https://checkip.amazonaws.com"
}

The example will retrieve the data at the URL.

[scottgerring]

I'll pick this up