Changeset spec filtering

Created by: LawnGnome

After descoping #15783 (closed) in the short term until our design team has more of a chance to figure out where we're going there, as an interim step towards an eventual design that integrates a filtering DSL into the text search box, we should port the existing dropdown filters from the campaign page over to the preview page to provide equivalent functionality.

The design for the spec dropdowns: https://www.figma.com/file/MxlqIj1eHeLrqr1BWGIXlL/Changeset-filter-design-%2316780?node-id=0%3A1&viewport=2732%2C1046%2C1