Metadata 4.5 - Add field to dataset DB for new publisher_obj

[svogt0511]

Purpose

Add rails db migration for metadata-4.5 to add the publisher_obj field to the dataset.

Related to: #1005

Approach

Open Questions and Pre-Merge TODOs

Learning

Types of changes

• Bug fix (non-breaking change which fixes an issue)

• New feature (non-breaking change which adds functionality)

• Breaking change (fix or feature that would cause existing functionality to change)

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