add support to do-release-upgrade for (EOL) kinetic/lunar to noble upgrades

[Impact]

Users stuck in kinetic, lunar, and mantic cannot upgrade to noble.

[Test Plan]

1. Perform an upgrade from kinetic

* First, create a jammy container and then manually upgrade it to kinetic:

$ lxc launch ubuntu:jammy j
$ lxc exec j bash
$ sed -i 's/archive.ubuntu.com/old-releases.ubuntu.com/g' /etc/apt/sources.list
$ sed -i 's/jammy/kinetic/g' /etc/apt/sources.list
$ apt update && apt dist-upgrade -y

[...]

* Now, try to upgrade:

$ do-release-upgrade

* This will fail with a message along the lines of "upgrades from kinetic to noble are not supported." Try with the version in -proposed, and it should work now:

$ do-release-upgrade --proposed

* This should run to completion.

2. Do a jammy -> noble upgrade to ensure no adverse side effects were introduced:

$ lxc launch ubuntu:jammy j
$ lxc exec j bash
$ do-release-upgrade --proposed

[Where problems could occur]

This patch changes the way From= is used in DistUpgrade.cfg. It now treats that field as a list and interprets it as allowable upgrade paths, instead of requiring a DistUpgrade.cfg.$series to exist for the current series.

This of course could disrupt existing upgrade paths, which is why the test plan requires a jammy->noble upgrade, too.

There were also other places in the code that used that From= field. These have been updated, but if any spots were missed, that could break existing logic.

[Original Description]

[Current Behavior]
Users still on Kinetic and Lunar are prompted to upgrade to Noble via the motd, however d-r-u claims that upgrading from those releases -> noble is unsupported. You also can not upgrade to mantic anymore, so you would need to manually change your sources to facilitate the upgrade.

[Expected Behavior]
Despite these releases being EOL, historically we have allowed d-r-u (hirsute->jammy for example).

[Replication Steps]
Launch a lunar instance, upgrade to latest packages, and call do-release upgrade

[Root Cause]
It appears that we're missing DistUpgrade.cfg.jammy for kinetic/lunar's UpgradeTools . Ideally we should fix this to allow easier upgrades to supported releases, as we had previously.