WIP: Add API to gracefully cancel a controller

[Rayman]

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Basic Info

Info	Please fill out this column
Ticket(s) this addresses	#4033
Primary OS tested on	Ubuntu
Robotic platform tested on	Gazebo simulation of inhouse robot
Does this PR contain AI generated software?	No

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Description of contribution in a few bullet points

Ability to let controllers handle cancelations gracefully. See the discussion at https://github.com/ros-planning/navigation2/issues/4033.

I'm opening this PR for a first review of the API. I've added gracefull cancellation to one of our in-house controllers and tested that this API is sufficient. I hope the API fits the design of the core APIs.

Description of documentation updates required from your changes

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Future work that may be required in bullet points

• [ ] Add gracefull cancellation to one of the existing controllers.

For Maintainers:

• [ ] Check that any new parameters added are updated in navigation.ros.org
• [ ] Check that any significant change is added to the migration guide
• [ ] Check that any new features OR changes to existing behaviors are reflected in the tuning guide
• [ ] Check that any new functions have Doxygen added
• [ ] Check that any new features have test coverage
• [ ] Check that any new plugins is added to the plugins page
• [ ] If BT Node, Additionally: add to BT's XML index of nodes for groot, BT package's readme table, and BT library lists