Staging draft submissions needs to change

[rjsparks]

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Currently there is a common shared directory that submissions are staged in, and it is exposed by the www.ietf.org webserver.

The reasons leading to this are all no longer relevant, and the way submission staging is handled needs to be redesigned.

Staging should happen in a way that only those that can approve the submission can access it, and should be cleaned away when the submission is approved, or when the submission expires (see #1514).

Currently, I think these should be captured in the database (and perhaps scrubbed from the developer dumps) rather than placed on the filesystem. Access to the staged artifacts for use during the approval process should occur only through the datatracker.

Guards against DOS/abuse of the submission/approval process should be re-examined during this change.