Dynamodb writeitem

[endgame]

Closes #798

@divarvel can you see if this is better for you?

• Changelog entry

[divarvel]

Thanks for the change! this makes things easier indeed.
The only thing i'm not sure of is the use of Data.Map (instead of Data.Map.Strict or a HashMap, which seem to be used a bit more in amazonka-adjacent code)

[endgame]

Data.Map.Strict is probably a good idea both here and with AttributeValue, but I think that moving towards Map of some kind is a good long-term move because a) you avoid accidentally-quadratic behaviour when merging many maps, and b) aeson's internal type for KeyMap switched over to Map.

[endgame]

Actually, it doesn't matter whether we import Data.Map.Lazy or Data.Map.Strict as we're only importing the type name.