Migrate certgen packaging test from bats (#50880)

This commit moves the packaging tests for elasticsearch-certgen
to java from bats. Although certgen is deprecated, the tests are
moved rather than just deleted, and the tests themselves should be
easily adaptable to certutil. One note is that the test is simplified to
use a single node, rather than the two node test from bats, which was
problematic given how the newer distro tests only operate with a single
distribution.

relates #46005

Author: rjernst