Consolidate how deployCesium works in gulpfile.cjs

[OmarShehata]

gulpfile.cjs in master will currently upload all files to a single upload location:

cesium/gulpfile.cjs

Line 455 in 7047852

return listAll(s3, bucketName, prefix, existingBlobs)

gulpfile.cjs in the cesium.com branch however needs to upload different directories to different upload locations, because Sandcastle lives at sandcastle.cesium.com, whereas the docs live at https://cesium.com/docs/cesiumjs-ref-doc/:

cesium/gulpfile.cjs

Line 466 in 0d17b12

function uploadFiles(prefix, filePrefix, files) {

This difference made it hard to resolve a merge conflict during release, see discussion in: #8715

We should consolidate how the gulpfile deploys Cesium to avoid conflicts like this.