feat: jan-git / jan-nightly AUR package

[OmegaLambda1998]

• I have searched the existing issues

Is your feature request related to a problem? Please describe it

Currently, jan is available in the Arch User Repository as a pre-built binary, and an appimage. The binary is (at the time of posting) jan version 0.5.1-1, whilst the appimage is version 0.4.11-1. It would be great to have a third options, which packages the nightly release too

Describe the solution

Create and maintain a PKGBUILD for the nightly release of jan.

Teachability, documentation, adoption, migration strategy

No response

What is the motivation / use case for changing the behavior?

Easier access to nightly release = faster access to new / experimental features, and faster turn-around for bugs