Account web UI migration tweaks

[byewokko]

Collection of tweaks and fixes made while migrating Seacat Account Webui (http://gitlab.teskalabs.int/ateska/webui-microfrontends-poc/-/merge_requests/148)

• Move GET /features endpoint under /account since it won't be used in public API anymore.
• FIDO credential name allows any character (it should be a human-palatable name).
• External login provider label contains only the display name of the provider, e.g. "AppleID" instead of "Sign in with AppleID".
• TOTP error responses now have error code 400.