custom action plugin with ConfigurationForm
You need to install the core module Actions first to be able to configure action plugins in UI.
Then you can access the actions overview page:
/admin/config/system/actions
On the top of the page your new plugin should be present in the select list for creating advanced actions. When you select the plugin you should see the configuration form of your plugin:
/admin/config/system/actions/add/action_plugin_examples_update_node_title
Since you have already provided an action configuration in a YAML file you should also see a configured instance of your plugin in the available actions list.