Call a webhook when a Remotion Lambda render is done #1006

🎃 This issue is part of our Hacktoberfest campaign! 📚 Read more about Hacktoberfest here 🕛 This issue is currently assigned to @paulkuhle!

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This was request by two Discord members: mindbugg and Allfather.

Hacktoberfest Acceptance criteria:

• Allow the user to pass a URL to renderMediaOnLambda() that is being called when a Lambda render is done.
• Post when the render succeeded, but also when it fails or is about to timeout (send shortly before the timeout will kill the Lambda function)
• Allow the user to verify the webhook request is authentic using a cryptographic check (google "stripe verify webhooks", "validate github webhooks", "validate hubspot webhooks" for examples). This cryptography must be sound.
• add the new options to the renderMediaOnLambda() documentation page
• make a documentation page that shows an example of how to use and validate webhooks.