config: remind user that no default account was set

[sauterp]

Description

❯ exo config add
[+] API Key [none]: asdf
[+] Secret Key [none]: asdf
[+] Name [none]: asdf
✔ at-vie-1
[+] Set [asdf] as default account? [yN]: N
no default account set

Checklist

(For exoscale contributors)

• [x] Changelog updated (under Unreleased block)
• [ ] Testing