Declare missing octovis dependency on opengl

[cottsay]

It appears that libGLU is an indirect dependency on Ubuntu, but not on RHEL/Fedora. Better to be explicit anyway.

Here's the rosdep key: https://github.com/ros/rosdistro/blob/f4e07369c9790cd890a4cb34c001c94e8d4aad69/rosdep/base.yaml#L6943C1-L6958

Here's where openGL is found:

octomap/octovis/CMakeLists.txt

Line 71 in 312f6b0

FIND_PACKAGE(OpenGL)

Here's where both libGL and libGLU are referenced:

octomap/octovis/CMakeLists_src.txt

Lines 104 to 105 in 312f6b0

	${OPENGL_gl_LIBRARY}
	${OPENGL_glu_LIBRARY}

This is why octovis is blocked on the ROS 2 buildfarm for RHEL.