[FEATURE] How to add a new planner tutorial

[ChamzasKonstantinos]

I noticed that several new OMPL planners are still not available in MoveIt here, especially from AO planners only three exist
I think we should
A) make a PR to MoveIt adding new planners such as AIT* and BIT* and
B) Add some scripts and documentation to show examples of adding a new OMPL (or not) planners in robowflex. For example using the access to simple setup.

[mamoll]

Re. A), this is likely several PRs, one for each ROS release you care about (which is typically tied to one OMPL <major>.<minor> release). I did this for melodic here in my own moveit clone for the HyperPlan work (the current version of this code in MoveIt is not as ugly, BTW). It'd be cool if MoveIt could just auto-discover all Planner-derived classes in the namespace ompl::geometric, instead of having to hard-code each planner type. That's probably not that easy; for instance, you'd also have to check whether the constructors have the right signature.