Improve error messages in front-end upon server failures

[pcrespov]

Long story short

All 4xx and 5xx errors shall be properly logged (see https://httpstatuses.com/ for details of every) considering the context of the front-end user!

Had a 404 (Not found) upon login in front-end is shown as Error while fetching auth and took me some time to realize that auth was the resource.

Expected behaviour

When webserver responds 404

 "POST /v0/auth/login HTTP/1.1" 404 172 "http://127.0.0.1:8080/" "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/80.0.3987.106 Safari/537.36"

front-end shall log something in the line of "Currently, it is not possible to login [404]" (the latter I would display only if tester (e.g. staging)

Actual behaviour

front-end is shown as Error while fetching auth

Steps to reproduce

• create config and disable all subsystems
• start webserver
• login

Your environment

dev mode

[pcrespov]

this is a cool 404 https://codepen.io/moso/pen/KEVPJO