Objectstore allow clearing entries on 404

[rullzer]

If for some reason the filecache has a file in there that is no longer on the objectstore we get back a 404 when we try to access that file.

since there is no way to scan the object store currently. It would be great to have the admin to set a flag to kill them.

CC: @icewind1991

[szaimen]

@icewind1991 I suppose this issue is still valid? If not, please close this issue!

[joshtrichards]

Related: #38226