Add api change log for replacing report_card.dataset with report_card.type (#39044)

* add an api change log about replacing report_card.dataset with report_card.type

* Update docs/developers-guide/api-changelog.md

docs/developers-guide/api-changelog.md

@@ -5,3 +5,6 @@ title: API changelog
 # Breaking changes to the API interface
 
 ## Metabase 0.49.0
+- `POST /api/card` and `PUT /api/card/:id`
+
+  The `dataset` key is deprecated and will be removed in a future version, most likely 50. In its place we have added a new key: `type` which is equivalent in that it distinguishes Models from Questions. `type="model"` is equivalent to `dataset=true` and `type="query"` is equivalent to `dataset=false`.
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