Fix configuring global illumination GUI plugin parameters

[iche033]

🦟 Bug fix

Summary

The Global illumination GUI plugin's parameters specified through SDF are currently parsed by the plugin but they have no effect. This PR fixes the issue for both plugins (Vct and CiVct).

To test, you can run this world:

gi_gui.sdf

<?xml version="1.0" encoding="UTF-8"?>

<sdf version="1.10">
  <world name="default">
    <gui fullscreen="0">
      <plugin filename="GlobalIlluminationVct" name="GI">
        <gz-gui>
          <property type="string" key="state">docked_collapsed</property>
        </gz-gui>
        <enabled>true</enabled>
        <highQuality>false</highQuality>
        <resolution>32 32 32</resolution>
        <octantCount>2 2 2</octantCount>
        <conserveMemory>false</conserveMemory>
        <thinWallCounter>1.1</thinWallCounter>
        <anisotropic>false</anisotropic>
        <bounceCount>7</bounceCount>
      </plugin>
    </gui>

    <model name="ground_plane">
      <static>true</static>
      <link name="link">
        <collision name="collision">
          <geometry>
            <plane>
              <normal>0 0 1</normal>
              <size>100 100</size>
            </plane>
          </geometry>
        </collision>
        <visual name="visual">
          <geometry>
            <plane>
              <normal>0 0 1</normal>
              <size>100 100</size>
            </plane>
          </geometry>
        </visual>
      </link>
    </model>
  </world>
</sdf>

and verify that the GI properties displayed in the GUI match those specified in SDF:

Checklist

• Signed all commits for DCO
• Added tests
• Updated documentation (as needed)
• Updated migration guide (as needed)
• Consider updating Python bindings (if the library has them)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
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