When no rules in the distribution matrix match, provide a fallback/default

As a workflow admin I want to be able to configure behaviour when no rules match in a distribution matrix.

As a workflow admin I want to be able to configure the workflow to "block" is no rules match and require input to resolve the situation. (e.g. to modify the workflow definition and then retry to apply the updated rules.)

E.g.

New metadata field values are added that are not covered by existing rules in the distribution matrix. Rather than the workflow block, we should be able to handle this case. (It is similar to gateways that have default paths.)