Automatically load required plugins for DriveToPoseController

[sauk2]

Desired behavior

The DriveToPoseController system plugin (#2679) currently requires the DiffDrive and OdometryPublisher plugins to be manually attached to the model entity. The controller fails to function without these.

To improve usability, these dependencies should be loaded automatically if they are missing.

Alternatives considered

The current implementation verifies the existence of required publishers/subscribers and logs an error message if they are unavailable before exiting from the Configure callback and shutting down initialization.

Implementation suggestion

Two possible approaches to automatically load the required plugins:

1. Using gz-transport: Send a request to the /entity/system/add service to load missing plugins dynamically, as shown in the following example implementation.

gz-sim/src/gui/plugins/environment_loader/EnvironmentLoader.cc

Lines 166 to 191 in af92e29

	auto worldName = nameComp->Data();
	msgs::EntityPlugin_V req;
	req.mutable_entity()->set_id(world);
	auto plugin = req.add_plugins();
	plugin->set_name(preload_plugin_name);
	plugin->set_filename(preload_plugin_filename);
	plugin->set_innerxml("");
	msgs::Boolean res;
	bool result;
	const unsigned int timeout = 5000;
	const auto service = transport::TopicUtils::AsValidTopic(
	"/world/" + worldName + "/entity/system/add");
	if (service.empty())
	{
	gzerr << "Unable to request " << service << std::endl;
	return;
	}
	if (this->dataPtr->node.Request(service, req, timeout, res, result))
	{
	gzdbg << "Added plugin successfully" << std::endl;
	}
	else
	{
	gzerr << "Failed to load plugin" << std::endl;
	}

2. Using LoadSdfPlugins event: Create entities for the missing plugins and use the ParentEntity component to attach them to the model entity.

gz-sim/include/gz/sim/Events.hh

Lines 57 to 62 in 13bf5be

	/// \brief Event used to load plugins for an entity into simulation.
	/// Pass in the entity which will own the plugins, and an SDF element for
	/// the entity, which may contain multiple `<plugin>` tags.
	/// Makre sure that you don't also connect to the LoadPlugins event.
	using LoadSdfPlugins = common::EventT<void(Entity, sdf::Plugins),
	struct LoadPluginsTag>;

Additional context

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