Use distro-packaged composer package

[maxhoesel]

Right now, this role installs composer from the official install script. In the future, it'd be nice if we could use the distribution-provided package instead.

Ubuntu 22.04, Debian 11 and 12 ship with Composer 2.x, however Ubuntu 20.04 still has 1.x in its repos.
Whenever we remove support for 20.04, we should remove the script install logic and just use the distro package instead.
Since /usr/local/bin overrides /usr/bin, this should be backwards-compatible.