feat: allow passing a validator function

[Garcel]

feat: allow passing a validator function to perform complex or customized validations on parameters.

Example:

NEIGHBORHOODS = {
    1: {'id': 1, 'name': 'Birloque'}
}

def is_valid_neighborhood_id(id: int) -> bool:
    return id in NEIGHBORHOODS

@app.route('/neighborhood/<int:id>', methods=['GET'])
@ValidateParameters()
def get_neighborhood(id: int = Route(func=is_valid_neighborhood_id)):
    return NEIGHBORHOODS.get(id)

[Ge0rg3]

Looks great, thank you for the PR!