cli.admin: Add an admin subcommand 'deposit reschedule'

swh deposit admin deposit reschedule --help

That only reschedules loading for now.

This command is for admin use since it needs writable access to the db.

Annex:

• cli.admin: Fix help message typo

Depends on !25 (closed) Related #1703 (closed)

Test Plan

tox + docker dev

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Migrated from D1447 (view on Phabricator)