Update API Changelog for trash

[johnswanson]

Adding the following to the Changelog:

Breaking changes to the API interface

Metabase 0.50.0

• PUT /api/dashboard/:id, PUT /api/card/:id, and PUT /api/collection/:id

  When setting archived to true, the Dashboard, Card, or Collection will be automatically moved to the Trash
  collection, a special collection that holds all archived items.

  When setting archived to false, you may optionally also provide a collection_id (for Dashboards or Cards) or a
  parent_id (for Collections). In this case, the entity will be re-parented to the specified Collection when it is
  moved from the Trash. If a new collection_id or parent_id is not provided, the entity will be moved back to its
  original location if possible. If this is not possible (for example, the original location is also in the Trash) an
  error will occur.

Metabase 0.50.0

• GET /api/collection/:id/items

  An additional boolean column, archived, has been added to results.