Simplify app development with dedicated API for tasks not depending on volatile process state

[Viir]

So far, we always use volatile processes to run tasks integrating other software.
However, in many cases, we don't need the facilities to retain volatile process state beyond a single task. Examples are usages of elm-format and elm make in Elm Editor.

A dedicated API for a single task would simplify application developers' implementation. For example, this part should be simpler (And more complete, forwarding any errors that were not linked to RequestToVolatileProcess):

pine/implement/example-apps/elm-editor/src/Backend/Main.elm

Lines 370 to 377 in e4949e0

	Err Platform.WebService.ProcessNotFound ->
	( httpResponseInternalServerError
	("Error: Volatile process '"
	++ pendingTask.volatileProcessId
	++ "' disappeared. Starting volatile process again... Please retry."
	)
	, Just pendingTask.volatileProcessId
	)