Need a set of tutorials with examples of creating new plugins. These shouldn't take long and should be very simple implementations as an example

• costmap 2d: gradient layer
• Planner: straightline planner
• Controller: Pure pursuit [IN PROGRESS]
• Recovery: Send a slack / sms message / email or something
• BT: Call new server to trigger an external action (call an elevator, hook into moveit, etc) I think we should have 1 for Action nodes using our wrapper (since that's tutorial-worthy itself) and one that's a raw node (decorator, condition, etc) that doesn't use one of our wrappers.