Fix serverless_example.md

[Hustenbonbon]

Fix the broken update from Node14 and AWS-SDK v2 to Node18 and AWS-SDK v3

Issue #, if available: #454

Description of changes:

• Changes the import in widgets.js to 'require' syntax, so it can run without a module scope.
• Also fix the first version of widget.js
• Adds a fix for changed S3 ListObjectsV2Command API behaviour if no objects exist
• Formatted with prettier (I'm happy to undo that, if you want to keep the changeset smaller)

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