## About the changes
Schedules a best-effort task setting the value of
events.created_by_user_id based on what is found in the created_by
column and if it's capable of resolving that to a userid/a system id.
The process is executed in the events-store, it takes a chunk of events
that haven't been processed yet, attempts to join users and api_tokens
tables on created_by = username/email, loops through and tries to figure
out an id to set. Then updates the record.
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Co-authored-by: Gastón Fournier <gaston@getunleash.io>
