Allow config/theme files with custom location

[webflo-dev]

Describe the feature

Actually, the config and theme files are loaded from a fixed path inside the user home.
It would be nice to have a CLI flag to allow a custom path for these files.

It should be implemented because

• It would unlock config generation with nixos without home-manager.
• It would allow using multiple configs and themes without playing with symlink or updating the files

Additional context

No response

Would you like to work on this issue?

Why not :)

[versenilvis]

just one command iris --config-dir [your-dir] is ok, right?

p/s: already opened new PR #146 and let it there until you reply to me