adds field mesh to gazebo with collision

[JakeWendling]

PR Summary

PR Link: INSERT-LINK-HERE

Description

Adds field mesh into gazebo with collisions

Reviewers

• Required: @MaxxWilson , @melissajcruz

• Optional: @xwilson03

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Changelog

• Adds field mesh and triball mesh files to 03_ROS/ghost_sim/urdf/meshes
• modifies spin_up.world to include the meshes
• added 2 paths to bashrc for this to work

Reviewer Guide

• run the simulator and make sure the lidar rays hit the walls

./scripts/launch_sim.sh

• make sure the robot isnt in the floor

[MaxxWilson]

Can you add the commands to run the code under Testing?

Something like "ros2 launch ..." that can be copy pasted into a terminal.

[MaxxWilson]

To my understanding, this had #27 merged into it, and thus we can't merge to develop until that PR goes through. So will revisit once the simulation fixes goes through.