Add changelog for openid resource addition

Signed-off-by: Jason Robinson <jasonr@matrix.org>

changelog.d/4420.feature

@@ -0,0 +1,13 @@
+New listener resource for the federation API "openid/userinfo" endpoint
+
+Integration managers use the OpenID userinfo endpoint in the federation API to verify that user
+OpenID access tokens are valid. If the federation resource is disabled, integration managers will not be able
+to verify the access token, causing a broken experience for users. The OpenID userinfo endpoint has now been split
+to a separate `openid` resource, which is enabled by default in newly generated configuration. It is also enabled
+automatically if the federation resource is enabled.
+
+If your homeserver runs federation enabled, this change does not require any actions.
+
+If you run a homeserver with federation disabled, we recommend adding the `openid` resource to your homeserver
+configuration in the `type: http` listener `resources` list to allow your users access to
+integration manager features.