Report Theme JSON Schema - publish 'reportThemeSchema-latest.json'

[ssmit-doc]

Publish a copy of the latest Schema as 'https://raw.githubusercontent.com/microsoft/powerbi-desktop-samples/main/Report%20Theme%20JSON%20Schema/reportThemeSchema-latest.json', to allow users to link to the most recent schema definition without needing to update "$schema": in their report theme each time a new revision is published.