This moves a few types and constants to the global package so it can be
used without importing the `task/backend` package. These constants are
referenced in non tasks-specific code.
This is needed to break a dependency chain where the task backend will
call into the flux runtime to perform parsing or evaluation of a script
and to prevent the http package from inheriting that dependency.
To have checks and notifications happen transactionally we need to be
able to alert the task system when a new task was created using the checks and notifications systems.
These two new middlewares allow us to inform the task system of a update
to a task that was created through the check or notification systems.
Jonathan A. Sternberg
Alirie Gray
Lyon Hill
Michael Desa
George