Implement a specific error type for API responses

[mssola]

How to test

$ make build
$ REGCODE=invalid ./out/public-api-demo SLES 15.6 x86_64

Then you will receive a proper message:

public-api-demo: A connect client library demo
1) Setup connection and perform an request
<- fetch token
-> update token
API error: Unknown Registration Code. (code: 401)

[felixsch]

lgtm 👍

How I reviewed this merge request:

• Checked the changes for things I want to suggest
• Ran the public-demo-api command and checked the error returned

As always, if you think I'm missing something which I should test, please let me know! 🚀

cheers,

PS: I'm wondering maybe in the future we should add different types of errors to make it more easy to distinguish between different errors. Is this a thing in golang land?