feat: serde dynamo

[hffmnn]

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🔥 Don't merge: this is rather experimental and up for discussion! 🔥 Note: So far I didn't deploy the API with theses changes so I am not sure, if it works as expected.

No issue, I wanted to try out serde_dynamo crate with the experimental support for the official aws-sdk.

Description of changes:

• Use serde_dynamo from_item and from_items and remove handcrafted From and TryFrom implementations
• Use serde_dynamo from_attribute_value and remove src/store/dynamodb/ext.rs

[nmoutschen]

Hey @hffmnn! Thanks a lot for creating this!

I think given that serde_dynamo is in alpha for support for the AWS SDK, we should probably hold merging this until it's stable, but it's definitively a great idea!