Add CloudFlare Workers receiver

[michaelgruner]

Summary

Implement a Cloudflare Workers receiver modeled after AwsLambdaReceiver.

Requirements

• I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.

[changeset-bot]

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Latest commit: 7ab3e01

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[salesforce-cla]

Thanks for the contribution! Before we can merge this, we need @michaelgruner to sign the Salesforce Inc. Contributor License Agreement.