Move changelog notes to the correct guides

doc/development/api_graphql_styleguide.md

@@ -1446,3 +1446,7 @@ For information on generating GraphQL documentation and schema files, see
 
 To help our readers, you should also add a new page to our [GraphQL API](../api/graphql/index.md) documentation.
 For guidance, see the [GraphQL API](documentation/graphql_styleguide.md) page.
+
+## Include a changelog entry
+
+All client-facing changes **must** include a [changelog entry](changelog.md).

doc/development/api_styleguide.md

@@ -292,3 +292,8 @@ expect(response).to match_response_schema('merge_requests')
 ```
 
 Also see [verifying N+1 performance](#verifying-with-tests) in tests.
+
+## Include a changelog entry
+
+All client-facing changes **must** include a [changelog entry](changelog.md).
+This does not include internal APIs.

doc/development/documentation/graphql_styleguide.md

@@ -90,7 +90,3 @@ Be aware that CI tests for that second MR will fail with a bad link until the
 main MR that adds the new GraphQL page is merged. Therefore, only merge the MR against the
 [`gitlab-docs`](https://gitlab.com/gitlab-org/gitlab-docs) repository after the content has
 been merged and live on `docs.gitlab.com`.
-
-## Include a changelog entry
-
-All client-facing changes **must** include a [changelog entry](../changelog.md).

doc/development/documentation/restful_api_styleguide.md

@@ -178,8 +178,3 @@ do something like this:
 ```shell
 curl --request PUT --header "PRIVATE-TOKEN: <your_access_token>" --data "skip_users[]=<user_id>" --data "skip_users[]=<user_id>" "https://gitlab.example.com/api/v4/projects/<project_id>/users"
 ```
-
-## Include a changelog entry
-
-All client-facing changes **must** include a [changelog entry](../changelog.md).
-This does not include internal APIs.