Improve ogre 1.x ThermalCamera to match ogre 2.x's implementation

## Desired behavior
The ogre1.x thermal camera implementation is missing a few features that are available in ogre2:
* color based temperature variation
* related ogre2 PR: #211
* support changing resolution/min/max at run time:
* related ogre2 PR: #1138
* more info in issue: #1134
* 8 bit + resolution support
* related ogre2 PR: #235

## Implementation suggestion
The pull requests above show these features in ogre2. We need to port them to ogre1.x.
* Here're ogre1.x's [material script](https://github.com/gazebosim/gz-rendering/blob/gz-rendering9/ogre/src/media/materials/scripts/thermal.material) and the [fragment shader](https://github.com/gazebosim/gz-rendering/blob/gz-rendering9/ogre/src/media/materials/programs/thermal_camera_fs.glsl) for the thermal camera.

Start by comparing the Ogre 1.x material script at ogre/src/media/materials/scripts/thermal.material and fragment shader at ogre/src/media/materials/programs/thermal_camera_fs.glsl with Ogre 2.x PRs #211, #1138, and #235. Trace issue #1134 for the runtime-resolution details. Done means Ogre 1.x supports color-based temperature variation, runtime resolution/min/max changes, and 8-bit output with resolution support.

Written by the indexing model from the issue text.