test: update the smoke test series/bases

[tonyandrewmeyer]

A collection of fixes for the smoke test:

• Update the smoke test charm to use the preferred "import ops" style.
• Fix tox to use "allowlist_externals" rather than "whitelist_externals", which doesn't work in recent versions of tox.
• Remove a bash comment in the tox smoke env - this didn't really add much value and on my system failed (I think tox believed everything after the # was a comment in tox, rather than in the bash statement)
• Drop support for bionic (18.04) and xenial (16.04). Modern charmcraft can't pack on these systems, because it requires a newer version of pip than is available for the system Python. We don't really support these any more either - at least not for using current versions of ops.
• Add support for jammy (22.04)
• Add support for noble (24.04) - this required a substantial change because of the required changes to charmcraft.yaml. Instead of having all the bases specified in a charmcraft.yaml that's in version control (which works fine for the older three), have the test generate a charmcraft.yaml that matches the required style for that base.
• Use pytest.mark.parametrize rather than putting the build and deploy in a single test - this is nicer from a logging/progress indication point of view, and generally cleaner for what are essentially subtests. Since modern charmcraft is building each charm separately (and especially now that it's using a separate yaml for each, to handle Noble) there isn't really any functional difference in terms of the test.
• When deploying, use base= rather than the deprecated series=

To test, run tox -e smoke (you'll need to have charmcraft, bash, and a Juju controller available).

[benhoyt]

Thanks for this!