Refactor/handle webhook

[gcharest]

Summary | Résumé

Breaking the handle_webhook function into a more manageable set of functions:

• if the payload is a string, it will be sent to the handle_string_payload for further processing.
• otherwise, the webhook payload is handled as usual

In the handle_string_payload, the string will be validated against known models (Webhook, AWS SNS, Access Request, Upptime)

• If it matches the Webhook model, it simply returns a Webhook payload
• if it matches an AwsSns model, it will be evaluated for validity.
  • once the payload is validated, the same handling of the type of AWS SNS payload is applied as before.
• if it matches the Access Request model, we don't perform anything specific at this point, just return a Webhook payload wiht the payload in the content of "text"
• if it matches the Upptime model, the downtime message will be parsed and returned for processing

[github-actions]

GitHub Action status on df00773 generated by comment-failure-action

Lint, format and test code

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[sylviamclaughlin]

Good work! 🎉