Refresh User cache when user is modified

[kubernetes-bad]

Redis cache is now refreshed when User is modified.

Problem:

After creating or deleting a shared key, it is not immediately reflected on /get_user endpoint as it serves now stale cached version.

This adds functionality to bust the user cache - both by id and by api_key - ensuring the cached results are always fresh.

How to test:

1. call GET /api/v2/find_user, you should see [] under sharedkey_ids
2. call GET /api/v2/users/:user_id, you should see [] under sharedkey_ids
3. call PUT /api/v2/sharedkeys with body {}
4. call GET /api/v2/find_user again, you should see ['5d81849a...'] under sharedkey_ids
5. call GET /api/v2/users/:user_id again, you should also see ['5d81849a...'] under sharedkey_ids
6. call DELETE /api/v2/sharedkeys/:keyId
7. call GET /api/v2/find_user, you should see [] under sharedkey_ids
8. call GET /api/v2/users/:user_id, you should see [] under sharedkey_ids