Fixes various issues

[aamster]

• add n_workers arg to vbn metadata writer module since database rejects when too many simultaneous connections
• convert date_of_acquisition read from DB in bulk read to UTC. This is being done when reading a single doa from pickle file, need to also do it when reading from the db. Otherwise, when values are added from pkl file (with utc tz) to the table, it drops type and it becomes object.
• Update expected columns in trace table, since 2 new columns added
• Update expected date of acquisition in test. It was updated due to https://alleninstitute-brainscience.atlassian.net/browse/DT-4141 . I checked the pkl file, and the update doa agrees.