Adding a tag must create a tag topic with "-tag" in the identifier

[Brett Alistair Kromkamp]

Currently, when adding a tag to a topic, Contextualise first checks if an accompanying tag topic exists; if the tag topic doesn't exist then a new tag topic is created with a slugified identifier equal to the tag string. What should happen is that the tag topic is created with an identifier that is made of both the slugified identifier part together with a "-tag" part.

[Brett Alistair Kromkamp]

This is a TopicDB bug and needs to be fixed there: https://github.com/brettkromkamp/topic-db/blob/master/src/topicdb/store/topicstore.py#L968