Update Dockerfile on the humble branch to use ROS humble

[adlarkin]

Description

The backport in e292e4d set the ROS_DISTRO to rolling for the humble branch, which would probably cause issues for users who are trying to go through the MoveIt2 tutorials with MoveIt2 humble. This PR sets the ROS_DISTRO to humble in the Dockerfile so that if users decide to use the Docker setup for the humble tutorials, ROS_DISTRO matches the MoveIt2 version.

Checklist

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[adlarkin]

@MikeWrock CI / humble-source is failing, and I'm not sure why. The error messages in GitHub actions mention struct planning_interface::MotionPlanResponse, but in humble, it looks like the PlanningComponent::Plan API call returns a PlanSolution struct instead. In rolling, the PlanningComponent::Plan API call does appear to return the planning_interface::MotionPlanResponse struct: https://github.com/ros-planning/moveit2/blob/00e10bbebdbef336aacd66fce3f2593844aee834/moveit_ros/planning/moveit_cpp/include/moveit/moveit_cpp/planning_component.h#L199-L201

So, it seems to me like the error stems from rolling code still being used somewhere. I tried modifying https://github.com/ros-planning/moveit2_tutorials/blob/adlarkin/humble_docker_version_fix/.github/workflows/docker-images.yml#L12 to only build humble and not rolling, but I am still seeing the same CI failures. It also looks like humble is used in the industrial_ci for this action (https://github.com/ros-planning/moveit2_tutorials/blob/adlarkin/humble_docker_version_fix/.github/workflows/ci.yaml), so I am not sure what is causing this issue at the moment.

[adlarkin]

I am going to close this PR - it turns out that for the CI builds that build and push updated tutorial Docker images, the ROS_DISTRO is correctly being set via a build arg (notice how there are build args for both rolling and humble, which means that a humble and rolling image will be built and pushed). The real issue here that's causing some of the humble Docker images to actually have rolling installed is upstream (moveit/moveit2#2035 (comment)). Once the upstream issue is resolved, we will probably need to re-build the tutorial Docker images since they depend on the upstream Docker images.

I have created an issue so that we can track the progress of getting the tutorial images fixed: #646