structured errors for connection failures

[vjeffrey]

In order to better consume the errors produced by cnquery/cnspec during scans, we need to start structuring these errors a bit more.
Specifically, we need to identify when an error is an auth-based error vs some other scan error.
This will help all consumers of cnquery to more appropriately respond to errors through automated systems.

example:
cnspec scan aws
-> results in auth error bc missing or expired creds

as an example, we could read the error and ensure the statusCode aligns to what we all expect/agree on to signify an auth error (401/403)

type cnqueryError struct {
statusCode int32
message string
}

the consumer of the error could then send a better message to the user about what went wrong/wrap the error message in a helpful way in automated scenarios

things to consider:

• this work is provider-specific