Provides the means to serve an error to the user with a user-friendly
error message (serveCustomJSONError). Auth API uses this when
processing registration attempts.
Previously, the error message was inferred by the client based on
the status code of the response received from the server. However,
if multiple distinct errors fit a certain status code, it was impossible
to correctly interpret the error.
Change-Id: I2f91e9c81ba1a4d14ba67e0b4b531a48800d4799
This change removes all the separate implementations for
`apiservice.serveJSONError()` and defines one for every service to use
in `consoleapi/common.go`.
Change-Id: Iabf184e5cba69a98eb25936ce11ebd07f02c8ff3
