Add collision sensors

[irisxu02]

Follow the sensors tutorial to add collision sensors on static objects.

• Update the sdf template for new worlds to include sensors and contact plugins
• Update the sdf template for new environment objects to include TouchPlugin
• [ ]

TouchPlugin tags:

• target: how do we make sure that all other objects/relevant objects that could potentially collide with the static object are included as "target"?
• namespace should match object name - requires updating scripts to make this change automatically upon loading new object.

Check if compatible:

    <plugin
      filename="ignition-gazebo-sensors-system"
      name="gz::sim::systems::Sensors">
      <render_engine>ogre2</render_engine>
    </plugin>
    <plugin filename="libignition-gazebo-contact-system.so"
        name="ignition::gazebo::systems::Contact">
    </plugin>

Usage:

• e.g. listen to collision topic e.g. ign topic -e -t /wall/touched

[irisxu02]

Write custom plugin to publish human-readable message containing information like contact point and entities that collided. For example, listen to topic /physics/contacts (should enable publishing to this from physics plugin)
then report a formatted message
"Collision detected between box::link::collision and wall::link::collision at position: (0.5, 1.2, 0.0)"