Support custom PKGBUILD repository other than AUR

[brainwo]

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

Managing multiple PKGBUILD repository is a pain without a helper.

Describe the solution you'd like

yay already pulls AUR package lists as aur repository. Ideally, supporting another PKGBUILD repository would do the same as AUR, but with another name and in another location, with the same method of installing PKGBUILDs from AUR using yay.

Describe alternatives you've considered

Switch to paru, but paru also lacks some feature I'm looking for, I prefer yay.

Additional context

How paru handles this:

https://github.com/Morganamilo/paru/blob/130a7c678610421a077659fbe1a70355c958d2f2/man/paru.conf.5#L388

In short, it allows you to add a new section in paru.conf just like in pacman.conf.

[mylocalpkgbuildrepo]
Path = /path/to/my/local/repo

[myremotepkgbuildrepo]
Url = https://path/to/my/remote/repo

[Jacoblightning]

There is a flag --aururl to specify another url.