add the ability to inject arguments into tasks at task creation

Similar to the rebind functionality that lets you rename parameters
from those in the store, inject lets you inject arbitrary key/value
pairs that will be sent to your task at task creation time.  This allows
for flow and flow factories to reuse tasks with differing parameters
without jumping through a lot of hoops.

Change-Id: If167962811d22054b89d7d35a33d4ec5cb2cd648
Implements: blueprint wbe-workers-endpoints-constructors
Merge "add the ability to inject arguments into tasks at task creation"