Consider the applicability of tags for the edge

[huntc]

From Patrik:

We have found that tags is a pretty good way to filter events (consumer defined filters, evaluated on producer side). Without tags those filters can only be on entity ids (exact or regex). I think we have been and still are uncertain about how useful consumer defined filters are for the case when edge is producer. I guess the consumer would be interested in all events from the edge in most cases, and the edge itself decides what to publish (producer defined filter). I would say that tag filters can be added when we have more important things in place. Also depends on effort, if it's a small thing to add tagging support we can just do it.

We now have a WithTags trait for envelopes. At present, it'll always return an empty vector.