RFE: apkg install

#24 (closed), packaging testing, and packaging automation in general require an ability to install produced packages on all supported distros. In Knot DNS and Resolver packaging tests, this is done by ansible but apkg already provides pkgstyles for different distros so it seems better to add apkg install command to install supplied packages using native distro package manager instead and evade Ansible dep entirely. apkg can be easily used from ansible, no need to create circular dependency.

In other words apkg install $PKGS will trigger apkg install $PKGS on Debian, dnf install $PKGS on Fedora etc.

This can be achieved by adding install_packages() function to individual pkgstyles.

I suspect being able to simply install packages without knowing distro-specific invocations will prove useful in many use cases outside of apkg testing.