fix(parser): loose validation on SNS fields to support FIFO

[heitorlessa]

Issue number: #1590

Summary

Changes

Please provide a summary of what's being changed

When enabling FIFO in SNS topics, SNS removes the following three keys leading to a ValidationError in Parser.

Error

SigningCertUrl
  none is not an allowed value (type=type_error.none.not_allowed)
Signature
  field required (type=value_error.missing)
SignatureVersion
  field required (type=value_error.missing)

This PR makes two changes:

• Marks all of these fields as Optional. In the future, we should look into having explicit FIFO Models to make strict typing better
• Removes test_handle_sns_sqs_trigger_event_json_body_missing_signing_cert_url that verified the field being tampered.. which is no longer valid due to FIFO behaviour completely removing this and other fields above

User experience

Please share what the user experience looks like before and after this change

Checklist

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• Meet tenets criteria
• I have performed a self-review of this change
• Changes have been tested
• Changes are documented
• PR title follows conventional commit semantics

Is this a breaking change?

RFC issue number:

Checklist:

• Migration process documented
• Implement warnings (if it can live side by side)

Acknowledgment

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[leandrodamascena]

Approved!!