* 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.
`lts` was choosen to reflect a "long term storage" but currently it's just an
object storage implementation. So use this term and "ost" as its abbreviation
(to not clash with "os").
* client: always parse the json error message field and return its contents
* Use ErrBadRequest and ErrNotFound in every handler and command
* Gateway: by default pass underlying service error (configstore, runservice) to
client keeping the status code and message. In future, if some errors must be
masked, we should change the specific parts that need special handling.
* Always return a json message also on error. For internal errors return a
generic "internal server error" message to not leak the real internal error to
clients
* Return 201 Created on resource creation
* Return 204 No Content on resource deletion and other action with no json
output
Simone Gotti