Add changelog entry for component's configuration

Entry covers multiple PRs and was missed when implementing the feature

Closes  #2885

CHANGELOG.md

@@ -70,6 +70,42 @@ $govuk-suppressed-warnings: (
 
 This was added in [#2911 Add warning suppression functionality](https://github.com/alphagov/govuk-frontend/pull/2911)
 
+#### Configure components in JavaScript
+
+JavaScript components receiving configuration through data attributes now accept the same configuration options when instantiated in JavaScript. These components are:
+
+- the `Button` component, for its `preventDoubleClick` option (matching `data-prevent-double-click`)
+- the `CharacterCount` component, for its `maxlength`,`maxwords` and `threshold` options (matching `data-maxlength`, `data-maxwords` and `data-threshold`, respectively)
+- the `ErrorSummary` component, for its `disableAutoFocus` option (matching `data-disable-auto-focus`)
+- the `NotificationBanner` component, for its `disableAutoFocus` option (matching `data-disable-auto-focus`)
+
+You can omit these options when calling the Nunjucks macro and provide them:
+
+- at component instantiation, in a configuration object as second argument, for example:
+
+  ```js
+  var button = document.querySelector('[data-module="button"]')
+  new GOVUKFrontend.Button(button, {preventDoubleClick: true})
+  ```
+
+- when initialising components in bulk using `initAll`, for example:
+
+  ```js
+  GOVUKFrontend.initAll({
+    button: {
+      preventDoubleClick: true
+    }
+    // Or, for the other components,
+    // characterCount: {/* options */},
+    // errorSummary: {/* options */},
+    // notificationBanner: {/* options */}
+  })
+  ```
+
+If you provide an option both through data attribute and JavaScript configuration, the components will use the value from the data attribute.
+
+This was added in pull requests specific for each components: [NotificationBanner – #2843](https://github.com/alphagov/govuk-frontend/pull/2843), [ErrorSumarry – #2854](https://github.com/alphagov/govuk-frontend/pull/2854), [Button – #2867](https://github.com/alphagov/govuk-frontend/pull/2867), and [CharacterCount – #2883](https://github.com/alphagov/govuk-frontend/pull/2883)
+
 ### Recommended changes
 
 #### Remove `aria-labelledby`, remove `id="error-summary-title"` from title and move `role="alert"` to child container on the error summary component