Support of Arch Linux in `getdeps.py`

## Info
Project support only `dnf` and `apt` package managers. I want to add `pacman` package manager support.

## Steps
- Add Arch distro and `pacman` package manager option for it
- Add `pps` (`pacman-packages`) option in `manifest.py`

## Pull request
#1702

Start with getdeps.py to trace how distro and package-manager options are represented, then inspect manifest.py for existing package options such as dnf and apt. Done means Arch Linux and pacman are supported and the pps (pacman-packages) manifest option is accepted; pull request #1702 indicates this work may already be underway.

Written by the indexing model from the issue text.