Geoff Lawler authored Feb 17, 2020 and Ryan Goodfellow committed Feb 17, 2020

The MergeError type can now be tranmitted via GRPC errors. So the
sequence is:

1. portal module generates a error
2. The error percolates up to the grpc service layer
3. The grpc service layer converts the error to grpc error
4. The client layer gets the error and recreates the MergeError
5. The API layer gets the MergeError and converts it to an API Error
6. The client gets the error as a http response, with JSON in the body
   and the appropriate error code.

There are 3 error formats at play here.

The MergeError type is based on RFC 7320
The GRPC Error is based on Google GRPC Error Codes
The Open API error HTTP status codes

And RFC 7320 is an "extention" of HTTP Status codes, so it's really like
2.5 error formats.

So there are things that don't quite fit. The general approach is that
if an error fits within an HTTP status (e.g. 404 Not Found), that will
work. If it does not ("Project already exists"), it will get mapped to a
400 HTTP Status and the body of the error will have the RFC 7320 fields