Prints each dependency that ships usage rules, and which sub-rule files exist.
Sub-rules are the basenames of deps/<app>/usage-rules/*.md (excluding skills/ trees),
consistent with mix usage_rules.sync.
Two errors can be raised normally. First is if the dependency is not in the project, then the "No dependency matching..." error will occur. The second error is if you have more than one argument. Only one dependency may be filtered at one time.
Examples
$ mix usage_rules.list
$ mix usage_rules.list ash