Autostarting lifecycle nodes and example launch file demo (backport #430)

[mergify]

This resolves #418 which implements autostarting lifecycle nodes. This is complete and ready for a review

You'll notice a couple of key changes worth explaining:

1. There is a new is_lifecycle_node attribute of the node and lifecycle nodes which is needed to remove a circular dependency on the LifecycleNode within the LifecycleTransition class which only is type checking. I replace this type check with checking if a non-None object (1) has the attribute at all and (2) has a lifecycle attribute with appropriate logging between the difference of a non-lifecycle node being attempted vs a non-node. This has been tested as well to function using the demos.

2. You will also notice that I refactored lifecycle node to have a separate util LifecycleEventManager, who handles the event emitting, handling, and topic listening for lifecycle nodes. This way, this can be used in lifecycle-components as well! No changes were made here except removing the self.__current_state variable which was completely unused. The LifecycleEventManager is only created if the node requests autostart at Launch time and otherwise has no overhead nor exposes the interfaces/event handler/emitter if its a non-lifecycle node.

3. The component nodes don't add a / before the node names with the namespaces. This messes with the node event matcher. I add in a leading / so that the action.node_name == node_name which has the / forcably applied in the node event matcher

4. I tested LifecycleNode, ComposableNodeContainer, LoadCompoableNodes for all cases: autostart=True autostart=False, and autostart field not supplied. You can also run any experiments you like using the 2 extra launch files I provide in the examples directory which shows all the features at work/

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   This is an automatic backport of pull request Autostarting lifecycle nodes and example launch file demo #430 done by Mergify.

[wjwwood]

@methylDragon if you have some time, could you review this backport with an eye towards likelihood of regressions in jazzy?

@SteveMacenski fyi