Global TTL

[ItsMrCube]

Storage can get expensive or run out over time when not managed correctly. I propose to have a global TTL setting implemented.
The setting would allow admins to make all existing and future uploads ephemeral based on a user-defined duration.

[diced]

Added in 78e884e. Available via the UPLOADER_DEFAULT_EXPIRATION variable, and supports the same values that work in the Expiry header.