Allow obfuscator to leave empty/null values as is

[mmed]

This is a Feature Proposal

Description

In the lambda-powertools-middleware-obfuscater package, would it be possible not to mask empty and null values?
This way we can tell whether value is given when investigating logs.

Given this example: (assume every field is blacklisted)

{
	"name": "John",
	"surname": "Smith",
	"address": "",
	"age": null
}

current output:

{
	"name": "*****",
	"surname": "*****",
	"address": "*****",
	"age": "*****"
}

suggested output:

{
	"name": "*****",
	"surname": "*****",
	"address": "",
	"age": null
}