AWS DynamoDB Scan operation requires FilterExpression

[mvhirsch]

Describe the bug
In the DynamoDB Node the Scan operation (Get All Items -> Scan) requires FilterExpression, which in fact is optional.

https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/Scan.html#Scan.FilterExpression

See also: https://community.n8n.io/t/aws-dynamodb-get-all-items/10375/4

Expected behavior
Field should be optional.

Environment (please complete the following information):

• OS: [e.g. Ubuntu Linux 18.04]
• n8n Version [e.g. 0.119.0]
• Node.js Version [e.g. 14.16.0]
• Database system [e.g. SQLite; n8n uses SQLite as default otherwise changed]
• Operation mode [e.g. own; operation modes are own, main and queue. Default is own]

Additional context