Add an option for a lifetime-only function manager

Description

The current function manager necessarily controls the lifetime of the xDAQ processes and the state transitions. This is fine and correct for normal runs with the GEM supervisors driven by the function manager; this is not adequate in some other cases:

• Stateless applications (e.g. monitoring suite)
• Configurations in which the GEM supervisor must not be supervised (e.g. local runs)

Possible fixes

A configuration option should be added to specify that the GEM function manager should only control the lifetime of the xDAQ processes, but not trigger state transitions.

An additional state should be envisioned in those cases: Initial -> Initializing -> Enabled (?)

Processes monitoring can be running as it should be in normal runs.