docs: Improve examples/cdk/README.md

[alex-m-aws]

Description of your changes

Write a dedicated readme that explains how to deploy and interact with the CDK examples. Also update stack identifiers, e.g. CdkAppStack, to more specific ones, e.g. 'LambdaPowertoolsTypeScript-ExamplesCdkStack', to consider users that are deploying this stack amongst others into their accounts.

The current README is just the default CDK TS readme and is therefore not helpful.

No dependencies for this change.

How to verify this change

Related issues, RFCs

#XXXXX
#ZZZZZ

PR status

Is this ready for review?: YES
Is it a breaking change?: NO

Checklist

• My changes meet the tenets criteria
• I have performed a self-review of my own code
• I have commented my code where necessary, particularly in areas that should be flagged with a TODO, or hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• The code coverage hasn't decreased
• I have added tests that prove my change is effective and works
• New and existing unit tests pass locally and in Github Actions
• Any dependent changes have been merged and published in downstream module
• The PR title follows the conventional commit semantics

Breaking change checklist

N/A

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[alex-m-aws]

@dreamorosi comments addressed in bd217ef