Add geometry_msgs/msg/VelocityWithCovarianceStamped (backport #323)

[mergify]

Description

Add the geometry_msgs/msg/VelocityWithCovarianceStamped.msg message to represent a fully-qualified velocity with uncertainty. This fills a gap between geometry_msgs/msg/VelocityStamped, which provides fully-qualified velocity without uncertainty, and geometry_msgs/msg/TwistWithCovarianceStamped, which provides convention-qualified velocity (implicit body and reference frames) with uncertainty. #322 describes this void in greater detail.

Fixes #322.

Is this user-facing behavior change?

Yes, this change adds a new message type to geometry_msgs which users will have access to. It does not modify any existing message types, so use of the new message type should be entirely "opt-in" with backwards compatibility preserved.

Did you use Generative AI?

No.

Additional Information

The new VelocityWithCovarianceStamped message intentionally duplicates the fields in VelocityStamped while adding the covariance field. There is no clean way that I see to either compose VelocityStamped within VelocityWithCovarianceStamped or break out common fields to a new message type (e.g., QualifiedVelocity) without either modifying existing message definitions or creating a non-standard message structure.

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This is an automatic backport of pull request #323 done by [Mergify](https://mergify.com).

[ahcorde]

Pulls: #334
Gist: https://gist.githubusercontent.com/ahcorde/30eb87e55f4c8f02577c1cd0a0136b7c/raw/8bfae0ab0a48395209ea4ac52c165487509934d9/ros2.repos
BUILD args: --packages-above-and-dependencies geometry_msgs
TEST args: --packages-above geometry_msgs
ROS Distro: lyrical
Job: ci_launcher
ci_launcher ran: https://ci.ros2.org/job/ci_launcher/19428

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