Refine Usage of Command Argument: stateful

[Vasileios-Mavroeidis]

The specification describes:

Note that if stateful is not explicitly set and the actuator only operates in either stateful or stateless the command would apply as if this argument was appropriately specified (e.g. stateful for Google Cloud Platform). If the actuator supports both mechanisms and this argument is not set, then it should treat the command as if the argument was set to stateless in order to be backwards compatible with the slpf.

Similar issue as #15

I suggest removing the second sentence as this is a default behavior handled by the actuator. This is a behavior that we should not dictate and it's a vendor's decision what would be the default state. If the actuator demands to specify the state then a command that does not have the argument stateful populated should be handled as an invalid command.

[Vasileios-Mavroeidis]

Or change to:

Note that if stateful is not explicitly set and the actuator only operates in either stateful or stateless the command would apply as if this argument was appropriately specified (e.g. stateful for Google Cloud Platform). If the actuator supports both mechanisms and this argument is not set, then it should treat the command based on its default behavior/approach or can respond back with Status Code 400 - Bad Request. Unable to process Command, parsing error.