Publish task files as an artifact revision [write]

Publishes paths from the task's file space (/tasks/{id}/files) as a new revision of the artifact with that name in the task, creating the artifact on first use. A path that names a folder publishes everything under it. The revision records each file's content at this moment; later edits to the task's files do not change it. entry defaults to the only file, or to an index.html. 400 when a path names nothing; at most 500 files.