Docs: Move the `Should I use this or Parser?` to the top of the Validation docs

[sdangol]

What were you searching in the docs?

Documentation regarding validation

Is this related to an existing documentation section?

https://docs.aws.amazon.com/powertools/typescript/latest/features/validation/#should-i-use-this-or-parser

How can we improve?

Right now, I would only know that the Parser package is recommended over the Validation package after reading through the Validation documentation and reaching at the end where I read the Should I use this or Parser?

Got a suggestion in mind?

The Should I use this or Parser? section should be at the top so that we know the recommended package is the Parser. Also would be nice to have something in the Parser docs which tells when when the Validation package should be used over Parser

Acknowledgment

• I understand the final update might be different from my proposed suggestion, or refused.