[SW-1483] Reorganize ROS 2 control packages

[khughes-bdai]

Change Overview

This PR splits the hardware interface for Spot into its own package in an effort to clean up the ros2 control work and make things more modular. The ROS 2 control relevant packages in this repo now are:

• spot_hardware_interface: contains custom hardware interface plugin
• spot_controllers: contains custom controller plugin (and would contain any future controller plugins we may want to have in this repo)
• spot_ros2_control: contains the main launchfiles for bringing up the hardware interface + controllers via ros2 control, also contains the examples

As a part of this I also updated the READMEs in these packages and moved some utility functions out of a header and into a .cpp file.

Testing Done

• [x] tested examples on robot and in mock. The interface for bringing up the ros2 control stack + running the examples has stayed the same.

[khughes-bdai]

• #511 👈
• main

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[coveralls]

Pull Request Test Coverage Report for Build 11443027494

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.1%) to 51.149%

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Totals
Change from base Build 11442440216:	0.1%
Covered Lines:	1937
Relevant Lines:	3787

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💛 - Coveralls

[khughes-bdai]

Merge activity

• Oct 21, 11:03 AM EDT: A user started a stack merge that includes this pull request via Graphite.
• Oct 21, 11:04 AM EDT: Graphite rebased this pull request as part of a merge.
• Oct 21, 11:17 AM EDT: Graphite couldn't merge this PR because it was not satisfying all requirements (Failed CI: 'Build and test spot_ros2 packages').
• Oct 21, 1:18 PM EDT: A user merged this pull request with Graphite.

[khughes-bdai]

@mhidalgo-bdai could I get another stamp on this? graphite force pushing this branch made the reviews stale 😭