Add additional checks on structured properties to not leak the additional properties to handlers during validation

[srujithpoondla03]

Description of changes:
Currently, in the provider definition schema we do not restrict the structured property to specify the additionalProperties as false. Structured properties should define the additionalProperties as false otherwise properties with different case or pattern could not be caught during validation.

Tested by running the cfn validate

⋊> ~/c/NrqlAlertCondition on master ⨯ cfn validate                                                                                                                                                       
[Warning] Resource spec validation would fail from next major version. Provider should mark additionalProperties as false if the property is defined as a structured property. Please fix the warnings: 'additionalProperties' is a required property

Failed validating 'required' in schema['properties']['definitions']['patternProperties']['^[A-Za-z0-9]{1,64}$']['allOf'][0]['dependencies']['properties']:
    {'$comment': 'An object cannot have both defined and undefined '
                 'properties; therefore, patternProperties is not allowed '
                 'when properties is specified.',
     'not': {'required': ['patternProperties']},
     'required': ['additionalProperties']}

On instance['definitions']['Term']:

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[priyap286]

Do we need to define what a structured property is? Also "additionalProperties" are a property of object schemas and are required only there.

[ammokhov]

lgtm

[PatMyron]

seems explicitly documented that additionalProperties should not be used:

"use of additionalProperties is not valid for a resource property"

Should try to check why that was documented and update that documentation if that's no longer the case

[srujithpoondla03]

Use of additionalProperties is not valid means provider should not model their schema to accept additionalProperties instead they should define all the properties or use patternProperties.

[PatMyron]

@srujithpoondla03 got it, maybe just re-worded to clarify then?