Bugfix: Return proper error

[avinassh]

• Bug:

client side errors were not getting properly mapped to the Twirp errors and defaulting to the Unknown error

• To Reproduce:

return any error from the server and client will print as unknown

• Cause:

When response status is not 200, we generate an error calling TwirpServerException.from_json, to this method, we send the error code as strings like invalid_argument or permission_denied. If you check TwirpServerException's constructor, it sorta expects code to be of error.Errors instance, if not, it defaults to Errors.Unknown error.

[ofpiyush]

The server exception implementation is wrong, it's supposed to check if the code is one of the available enum values only, not an instance