Proposal: Expose backup and restore functionality over management API (or C bindings)

The 7.0.0 release added support for the management API (https://apple.github.io/foundationdb/special-keys.html#management-module) which allows to programatically execute different tasks on a cluster without running `fdbcli`. It would be create if the same functionality would be implemented for for `fdbbackup` and `fdbrestore` this would allow users to program the whole life-cycle of a FoundationDB without calling any external binaries.

Start with the management API described in the linked special-keys documentation, then compare the requested fdbbackup and fdbrestore functionality with the existing fdbcli workflows. Done would mean users can programmatically manage backup and restore without invoking external binaries, either through the management API or C bindings.

Written by the indexing model from the issue text.