Re-order Executor initialization to prevent a ROS2 bug

[AbduEhab]

Description

I'm specifically talking about this issue: moveit/moveit2#1474. I only changed the order in which code is executed by creating the MoveGroup Interface before the executor.

The format of the code was not changed. The text explaining what the code does was also changed to represent the newly added/removed lines.

[AbduEhab]

Should I change it in all other tutorials involving RViz?

[AndyZe]

I'd appreciate it if you made a similar change for the other tutorials that have this issue. Brett started a list of them here but maybe there are others:

https://answers.ros.org/question/404996/moveit2-tutorials-getting-stuck/

move_group_interface_tutorial, motion_planning_api_tutorial, and motion_planning_pipeline_tutorial

[AbduEhab]

I have changed the 3 source files you specified to accommodate the temp fix. I will open a new pull request if I personally encounter any more issues with the MoveGroups and the executor.

[AndyZe]

I went ahead and fixed a build issue and a minor formatting issue, then pushed to a branch of my own since I didn't have permission to push to your branch. Don't worry, you're still marked as the author of the PR. The new PR is here: #516

In the future, I'd encourage you to checkout pre-commit to do formatting automatically. It's a great tool! Documented here:

https://moveit.ros.org/documentation/contributing/code/