* runservice: use generic task annotations instead of approval annotations
* runservice: add method to set task annotations
* gateway: when an user call the run task approval action, it will set in the
task annotations the approval users ids. The task won't be approved.
* scheduler: when the number of approvers meets the required minimum number
(currently 1) call the runservice to approve the task
In this way we could easily implement some approval features like requiring a
minimum number of approvers (saved in the task annotations) before marking the
run as approved in the runservice.
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