implement DynamoDBDerivedTypeAttribute for polymorphism support

[irina-herciu]

implement DynamoDBDerivedTypeAttribute for polymorphism support that should solve Saving nested items with class hierarchies #2985

Description

New DynamoDB PropertyAttribute added as DynamoDBDerivedTypeAttribute in order to add support for polymorphic types serialization and deserialization
[DynamoDBDerivedType("B", typeof(B))]

Type Attribute name can be configurable from DerivedTypeAttributeName on DynamoDBContextConfig and by default uses "$type".

Motivation and Context

#2985

Testing

Integration tests added

Screenshots (if appropriate)

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• My code follows the code style of this project
• My change requires a change to the documentation
• I have updated the documentation accordingly
• I have read the README document
• I have added tests to cover my changes
• All new and existing tests passed

License

• I confirm that this pull request can be released under the Apache 2 license

[normj]

@irina-herciu Can you make this change off of a branch based on v4-development? We have done a lot of work in V4 for supporting Native AOT with the DDB high level libraries and I want to make sure this feature doesn't break any of that work.

I'm also asking around other SDK's if they support nested polymorphic types. If there is a prior pattern we should considered that and I'm wondering what would be the cross SDK story for this. Meaning a type saved with the .NET libraries and then loaded from the Java DynamoDB mapper.