Every time we change `installer.sh`, run it in a few docker
containers based on different Linux distros, just as a simple test.
Also includes a few changes to the installer script itself to make
installation work in docker:
- install dnf config-manager command before running it
- run zypper in non-interactive mode
- update pacman indexes before installing packages
Updates https://github.com/tailscale/corp/issues/8952
Signed-off-by: Anton Tolchanov <anton@tailscale.com>
