Feature: Tags for flags #175

I as a busy product manager in order to easier manage the features of a particular software in my organisation's portfolio, I want to add tags and see tags in the UI.

Acceptance Criteria:

1. arbitrary number of tags can be added to a flag via the
2. All added tags are shown on the respective flags in the UI
3. Bonus: Clicking on a tag filters the list to include only flags with that tag (there is a way to disable the filter)