refactor: errors

[chesedo]

Description of change

We used to have code that went from ApiError -> ErrorKind -> ApiError. During this conversion to ErrorKind we would remove friendly errors which would have been helpful to our end users. So this removes the ErrorKind enum.

Instead, each module has its own Error know and knows has to convert it to ApiError to be as friendly as possible while not exposing sensitive information to users.

With this it is also easier to isolate the proxy errors so they now return a custom 600 error code if the proxy fails

How has this been tested? (if applicable)

Starting the local stack

[oddgrd]

This looks great, thanks for cleaning this up, Pieter! I left a few minor comments and some questions to further my own understanding. I think splitting the error up by modules is a great idea, and it's something we're trying to do in the new crates as well. We should be able to use the ApiError there as well.

[oddgrd]

Thanks!