Use CloudFront + Lambda function URL, removing API Gateway

[tmokmss]

With this update, we can now achieve the following:

• requests that take more than 30 seconds
• response streaming
• Lower Fargate cost (no charge on idle for api and web)
• Truly scalable compute thanks to Lambda

The drawback of this change:

• Increased cold start (up to 30 seconds on initial request)
  • maybe we can add OPTIMIZE_COLD_START flag to Dify
• Lambda's payload size limit is 6MB.
  • With base64 encoding, we can only upload files less than ~4.5MB.
  • Due to L@E restriction, currenlty we can only upload files up to 1MB! (ref)

The Dify Sandbox cannot run on Lambda, because we cannot access several commands or systemcalls that are required to create a sandbox.

[tmokmss]

We will merge this once for posterity... but revert it immediately because it is not ideal.