Expose toggle publish plug-in settings for Maya Look Shading Engine Naming

[BigRoy]

Brief description

As per request of Dillon Sindon (Lucan) on Discord here's a PR to expose the enabled status for the Maya Look Shading Engine Naming Validator.

Description

The first step was to add it to the project settings definition in: openpype/settings/entities/schemas/projects_schema/schemas/schema_maya_publish.json
By using the validator's class name: ValidateShadingEngine

        {
            "type": "schema_template",
            "name": "template_publish_plugin",
            "template_data": [
                {
                    "key": "ValidateShadingEngine",
                    "label": "Validate Look Shading Engine Naming"
                }
            ]
        },

After that we needed to generate the "default" settings for OpenPype. The easiest way to do so is to run the tools/run_settings tool provided with OpenPype code base. In there browse to the project settings and modify the defaults for this new entry. Save the settings.

This will update the relevant defaults .json - in this case: openpype/settings/defaults/project_settings/maya.json
That's all there is to it to expose settings for a publish plug-in.

[mkolar]

Thank you @BigRoy merging.