[Feature]: support XDG_CONFIG_HOME path for config file

[Crocmagnon]

Is there an existing issue for this?

• I have searched the existing issues

Product concerned

CLI config

Feature description

Support the XDG_CONFIG_HOME spec for the config file location (most often $HOME/.config/[subdir])
https://specifications.freedesktop.org/basedir-spec/latest/

[cgoesche]

This will most likely require equal modifications of go-ovh, otherwise the API client initialization will fail. Because the http client initialized in internal/http/client.go calls ovh.NewDefaultClient() which will read configuration from its own list of config paths, luckily, as of now is the same as this package's.