[Renderer] Alway have an alpha channel in beauty.

We would like the Beauty output to always have an alpha channel.

Current behaviour:

• If Alpha (Output) is ticked the Beauty (Image) has an alpha channel and the Alpha image sequence gets written. ✅
• If Alpha (Output) is NOT ticked the Beauty (Image) doesn't have an alpha channel and the Alpha image sequence is not written. ❌

This is because Modo requires an alpha output enable to calculate the alpha, regardless of wether it writes the image on disk or not.

Desired behaviour:

• If Alpha (Output) is ticked the Beauty (Image) has an alpha channel and the Alpha image sequence gets written. (NO CHANGE) ✅
• If Alpha (Output) is NOT ticked the Beauty (Image) has an alpha channel and the Alpha image sequence is not written. ✅

Annex:

Here's a test scene to launch the render. You can launch Asset pass beauty and the result should be (eventually) a sphere with alpha channel: ed249c91-49f3-4483-b10b-6990a2c44261

And here's a scene setup so that the beauty renders with alpha, note that the alpha output is enable but has no path: 1a10341b-0bf5-4673-a673-d29b1f6adaae

you can find the resulting images here:

\\studio\jobs\STU247_SaCartoon2\LIBRARIES\ASSETS\CHARACTERS\CooperA\RENDERS\LOOKDEV\BipDebug\Asset\v010\Beauty

CooperA_LOOKDEV_BipDebug_v010_AssetBeauty_1001.exr is from the first scene CooperA_LOOKDEV_BipDebug_v010_AssetBeauty_10011001 is from the second one