Add userId to log events

[tlanfer]

To follow a specifc users actions throughout logs, we want to add the users ID to log events. We pseudonymize the userId using a sha256 hash to preserve some privacy.

The changes in this PR contain everything to add userIds to log events in Go applications:

• An extension of the log schema
• A direct method to add userIds to log events
• A hook which uses a getter function to dynamically retrieve the userId fromt he current context, hash it, and add it to log events. This hook is designed to be compatible with our IDP client and its middleware functions