Publish State Path to ROS Topic when entering a State

[tropappar]

Publish the current state path on the topic flexbe/behavior_update when entering a state.

[DariusPietschatConbotics]

Just fyi this pull request won't work. After the merge every custom state has to define the onEnter method. A simple fix is not to remove the definition of onEnter.

[dcconner]

This seems reasonable with the fix of leaving onEnter with pass defined. I will plan to make this change on the FlexBE repo (https://github.com/FlexBE/flexbe_behavior_engine/issues) over the next week or so to both ROS 1 develop branch, and the ros2-devel branches on the FlexBE repo. Then close this PR. I do NOT plan to update this older repo.

Follow FlexBE/flexbe_behavior_engine#9 for future developments