Provides a simple endpoint for retrieving a "freshness tag." Similar to HTTP Etags, you should request this tag periodically and store it in your app's datastore. This can be used to determine if any skills data has been updated on the SkillsEngine side since the last time you checked. If it hasn't, and you know that YOUR request data has not changed, then there's no need to make that same request, potentially saving you (and us!) many computationally-expensive requests that would just return the same data as last time.