Update variables based on updated RViz Quickstart variable names

[Jakeisthesnake]

[Disclaimer: beginner. Just throwing out suggestions based on discrepancies (I think) I am seeing in the tutorials.] In the quick start tutorial, manipulator became panda_arm. Based on: https://github.com/ros-planning/moveit2_tutorials/pull/886

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[Jakeisthesnake]

Whoops, looks like there is a different tutorial for different branches. Closing since I think I missed something.