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)