Consume ghtorrent events as oneshot tasks with priority normal

Stream the ghtorrent events [1] to update the scheduler's updated model with new priority oneshot tasks.

• As a requisite, we need to provide one ssh public key as a PR [2].

• [1] http://ghtorrent.org/streaming.html

• [2] https://github.com/ghtorrent/ghtorrent.org/pull/437

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Migrated from T1051 (view on Phabricator)