* Create an APIError that should only be used for api returned errors.
It'll wrap an error and can have different Kinds and optional code and
message.
* The http handlers will use the first APIError available in the
error chain and generate a json response body containing the code and
the user message. The wrapped error is internal and is not sent in the
response.
If no api error is available in the chain a generic internal
server error will be returned.
* Add a RemoteError type that will be created from remote services calls
(runservice, configstore). It's similar to the APIError but a
different type to not propagate to the caller response and it'll not
contain any wrapped error.
* Gateway: when we call a remote service, by default, we'll create a
APIError using the RemoteError Kind (omitting the code and the
message that usually must not be propagated).
This is done for all the remote service calls as a starting point, in
future, if this default behavior is not the right one for a specific
remote service call, a new api error with a different kind and/or
augmented with the calling service error codes and user messages could
be created.
* datamanager: Use a dedicated ErrNotExist (and converting objectstorage
ErrNotExist).
Export clients and related packages.
The main rule is to not import internal packages from exported packages.
The gateway client and related types are totally decoupled from the gateway
service (not shared types between the client and the server).
Instead the configstore and the runservice client currently share many types
that are now exported (decoupling them will require that a lot of types must be
duplicated and the need of functions to convert between them, this will be done
in future when the APIs will be declared as stable).
