chore(docs): Update migration guide to add more info about image resolvers

docs/docs/reference/graphql-data-layer/schema-customization.md

@@ -1100,76 +1100,3 @@ data.allTeamMember.nodes.map(node => {
 ```
 
 > Note: All types implementing a queryable interface must also implement the `Node` interface
-
-## Extending third-party types
-
-So far, the examples have been dealing with types created from locally available data.
-However, Gatsby also allows to integrate and modify third-party GraphQL schemas.
-
-Usually, those third-party schemas are retrieved from remote sources via introspection
-query with Gatsby's `gatsby-source-graphql` plugin. To customize types integrated from
-a third-party schema, you can use the [`createResolvers`](/docs/reference/config-files/gatsby-node/#createResolvers) API.
-
-### Feeding remote images into `gatsby-image`
-
-As an example, you could look at [using-gatsby-source-graphql](https://github.com/gatsbyjs/gatsby/blob/master/examples/using-gatsby-source-graphql/gatsby-node.js) to see how you could use `createResolvers` to feed images from a CMS into `gatsby-image` (the assumption is that `gatsby-source-graphql` was configured
-to prefix all types from the third-party schema with `CMS`):
-
-```js:title=gatsby-node.js
-exports.createResolvers = ({
-  actions,
-  cache,
-  createNodeId,
-  createResolvers,
-  store,
-  reporter,
-}) => {
-  const { createNode } = actions
-  createResolvers({
-    CMS_Asset: {
-      imageFile: {
-        type: `File`,
-        resolve(source, args, context, info) {
-          return createRemoteFileNode({
-            url: source.url,
-            store,
-            cache,
-            createNode,
-            createNodeId,
-            reporter,
-          })
-        },
-      },
-    },
-  })
-}
-```
-
-You create a new `imageFile` field on the `CMS_Asset` type, which will create `File`
-nodes from every value on the `url` field. Since `File` nodes automatically have
-`childImageSharp` convenience fields available, you can then feed the images from the CMS
-into `gatsby-image` by querying:
-
-```graphql
-query {
-  cms {
-    post {
-      # In this example, the `post.image` field is of type `CMS_Asset`
-      image {
-        # It is important to include all fields in the query which you want to
-        # access in the resolver. In this example make sure to include
-        # the `url` field. In the future, Gatsby might provide a `@projection`
-        # extension to automatically include those fields.
-        url
-        imageFile {
-          childImageSharp {
-            fixed {
-              ...GatsbyImageSharpFixed
-            }
-          }
-        }
-      }
-    }
-  }
-}
-```

docs/docs/reference/release-notes/migrating-from-v3-to-v4.md

@@ -252,6 +252,8 @@ The recommended approach is to always create nodes in `sourceNodes`. We are goin
 this workaround that will work using `sourceNodes`. It is still being worked on, please post your use-cases and ideas
 in [this discussion](https://github.com/gatsbyjs/gatsby/discussions/32860#discussioncomment-1262874) to help us shape this new APIs.
 
+If you've used this with `gatsby-source-graphql`, please switch to [Gatsby GraphQL Source Toolkit](https://github.com/gatsbyjs/gatsby-graphql-toolkit). Generally speaking you'll want to create your own source plugin to fully support such use cases.
+
 You can also learn more about this in the [migration guide for source plugins](/docs/reference/release-notes/migrating-source-plugin-from-v3-to-v4/#2-data-mutations-need-to-happen-during-sourcenodes-or-oncreatenode).
 
 ### Changes to built-in types