Provide a flag or configuration option to allow `asdf install` to continue when missing plugins are found in .tool-versions

> I think we should stop installing when a missing plugin is encountered. Some projects define plugins in the order they must be installed in, because certain plugins depend on others. Proceeding to install subsequent versions after a plugin is not found could cause problems.

This change breaks my workflow as I intentionally do not install all plugins on all my machines (depending on which I need). Is there any way to disable this feature (looking at the code I guess no) or make it so it can be disabled?

_Originally posted by @cmur2 in https://github.com/asdf-vm/asdf/issues/1033#issuecomment-991784380_

Start at the `asdf install` handling for missing plugins and review how `.tool-versions` entries are processed. Compare the behavior described here with issue 1033, then define the option's expected behavior so users can continue past missing plugins without changing the existing default ordering and stopping behavior.

Written by the indexing model from the issue text.