Let AnyOf constraint report itemized causes on violation

If this is not desirable in a particular context, the error message
template can be overwritten via a `WithDescription` wrapper.

Author: mih

datalad_next/constraints/base.py

@@ -191,7 +191,7 @@ def __call__(self, value):
         self.raise_for(
             value,
             # plural OK, no sense in having 1 "alternative"
-            'not any of {n_alternatives} alternatives',
+            'not any of {n_alternatives} alternatives\n{__itemized_causes__}',
             # if any exception would be a ConstraintError
             # this would not be needed, because they
             # know the underlying constraint