The ? optional syntax for config actions breaks recipe validation

Problem/Motivation

In #3552023: Recipes should support skipping config actions on entities that don't exist, the recipe system added support for "optional" config actions -- that is, config actions that don't run if the entity they are targeting doesn't exist.

The problem is, we forgot to update the recipe validation logic to account for the possibility of config action entity names starting with ?. This means, if you try to use this syntax, the recipe will immediately break with a message like this:

Config actions cannot be applied to ?user.role.content_editor because the ?user extension is not installed, and is not installed by this recipe or any of the recipes it depends on.

Proposed resolution

Fix the validation logic to strip out the leading ? from config action targets.