[Theme request] Add Athena OS

You can find the OS information of Athena OS here: https://github.com/Athena-OS/athena-iso

For the banner text you can use (on Gitlab light theme the text could seem invisible because of transparent png):

As logo:

As small icon:

If you need the original photoshop files or other images, I can provide them to you.

Thank you in advance.