lambda-durable-human-approval-sam: Fix hardcoded API Gateway URL by using environment variable

[kakakakakku]

Issue #, if available:
N/A

Description of changes:
Hi😀 Thanks for the useful patterns!

While testing lambda-durable-human-approval-sam, I could not access to the Approval URL because url was hardcoded in Python code like below.

Check

I fixed it using environment variable and it works good 👍

$ curl -X POST https://o4asvvo0ok.execute-api.us-east-2.amazonaws.com/prod/requests \
  -H "Content-Type: application/json" \
  -d '{
    "requestId": "REQ-001",
    "amount": 5000,
    "description": "New server purchase"
  }'
  {"message": "Request accepted"}%     

Thank you😀

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[kakakakakku]

note: It's wrong url

[kakakakakku]

note: Update CloudWatch Logs log group name because I set FunctionName in SAM template

[kakakakakku]

note: To pass the API_BASE_URL environment variable to the Lambda function, we needed to resolve a circular dependency between the Lambda function and API Gateway. To break this cycle, we explicitly set the Lambda FunctionName and manually constructed the ARN in the API Gateway integration URI. This reduces the dependency to a one-way reference from the Lambda function to API Gateway, resolving the circular dependency😀

[kakakakakku]

note: Here is hardcoded API Gateway URL