feature: Store config in XDG conform location

[patrickpichler]

Checklist:

• I've searched for similar issues and couldn't find anything matching
• I've discussed this feature in the #k8sgpt slack channel

Is this feature request related to a problem?

• Yes
• No

Describe the solution you'd like

The config file should be stored in an XDG conform location. I would suggest the XDG_CONFIG_HOME folder,
which would be ~/.config on linux.

There is even a neat golang library which offers standardized locations for mac, windows and linux:
github.com/adrg/xdg

Benefits for the project and its users

This would help keeping the users home directory clean and be more inline with other applications installed.

Potential drawbacks

The config file location changes, so this would be a breaking change. We could still support
the old location for some time though or offer an automatic migration.

Additional context

Here is some more information about XDG: https://wiki.archlinux.org/title/XDG_Base_Directory