Allow re-installing old/broken tool installations following a plugin update, e.g. via post-plugin-update hook

[nirvana-msu]

Is your feature request related to a problem? Please describe.
Sometimes you make updates to your plugin that fix something that was broken in the previous installs. In these cases, it would be great to have a way to force re-installation of the old (broken) installs.

Describe the solution you'd like
One way to achieve that would be by adding a post-plugin-update hook - so that once plugin is updated, it can trigger re-installation of old (broken) installs. One tricky part would be to ensure re-install is only triggered when plugin is updated to a certain revision - e.g. next update may not require re-install. It would have been easy if plugins themselves were versioned, but I suppose it could also be done if we know which git-ref we're upgrading from.

Alternatively, this could be addressed by allowing a plugin to "declare" that a change breaks certain install versions - and then asdf itself could take care of re-installing those versions (if installed).

The hook is more general so can probably cover some other use-cases not described here.

Describe similar asdf features and why they are not sufficient
There are already similar hooks post-plugin-add and post-plugin-remove, but in this case an action needs to be taken on plugin update.

Describe workarounds you've considered
At the moment I have to warn users that they need to manually re-install affected tool versions after updating plugin.