Update user cache when user tags are updated

While working on pleroma-fe!595 (merged), I’ve noticed that tag updates weren't always reflected on FE immediately (Video: https://cl.ly/648e0818ae2e). Further debugging showed this was because views often use cached users and hence those records often contain old tags. The MR fixes it by updating the cache on tag-related actions. This also makes MRF tag policy work as soon as MRF tag is added to the user since TagPolicy uses cached user record and hence cached tags.