Add gazebo namespace

[delihus]

Added multiplerobot simulation with namespaced robots in Gazebo Ignition.

Added tests in Ignition for the camera and the range sensors.
bump::minor

Dependencies:
husarion/ros_components_description#39
husarion/husarion_controllers#4
delihus/ros2_controllers#1
husarion/husarion_gz_worlds#5

[rafal-gorecki]

That's all for now. Will review the tests soon.

[rafal-gorecki]

Is it a way to do not create new property?

[delihus]

When there is namespace_ext it throws:

[ros2-19] [ruby $(which ign) gazebo-1] terminate called after throwing an instance of 'rclcpp::exceptions::InvalidNamespaceError'
[ros2-19] [ruby $(which ign) gazebo-1]   what():  Invalid namespace: namespace must not end with a '/', unless only a '/':
[ros2-19] [ruby $(which ign) gazebo-1]   '/robot3/'

When there is namespace it gives None as namespace.

So the first approach is:

<xacro:unless value="${namespace == 'None'}">
  <namespace>${namespace}</namespace>
</xacro:unless>`

and the second with gz_control_namespace used the if condition on the begin of the file.

[rafal-gorecki]

Looks ok