FIX: Restructure temp/ folders for direct S3 uploads (PR #14137)

Previously we had temp/ in the middle of the S3 key path like so

  • /uploads/default/temp/randomstring/test.png (normal site)
  • /sitename/uploads/default/temp/randomstring/test.png (s3 folder path site)
  • /standard10/uploads/sitename/temp/randomstring/test.png (multisite site)

However this necessitates making a lifecycle rule to clean up incomplete S3 multipart uploads for every site, something which we cannot do. It makes much more sense to have a structure with /temp at the start of the key, which is what this commit does:

  • /temp/uploads/default/randomstring/test.png (normal site)
  • /temp/sitename/uploads/default/randomstring/test.png (s3 folder path site)
  • /temp/standard10/uploads/sitename/randomstring/test.png (multisite site)