Implement upsert and upsertAsync

[podlech]

upsert and upsertAsync use UpdateItem behind the scenes which allow to create or update an item in DynamoDB.

[kyeotic]

Hey @podlech, thanks for putting this together, its always nice to see people take an action-first approach in OSS. I know partial-updates with UpdateItem are a gap in the tempest API, and they are something I would like to get to.

Unfortunately, this API breaks some key principles in tempest. First, it directly exposes the AWS API UpdateItemEnhancedRequest, which tightly couples tempest's update to AWS's update. Second it gives up the strong type-safety of the View API it extends, allowing items of any type to be updated on a view, and requiring interaction with the low-level codec API to interact with items even when they are a part of the view being used.

Tempest reason-for-being is to provide an idiomatic-kotlin API with strong type safety. An UpdateItem API would need to adhere to this principle.

[Xin-Tong]

Looks good to me in the scope of down stream services. Defer to kyeotic from tempest point of view.

[podlech]

We'll try saveWithResult and report back.