Make "Value Changed" processor dimension sensitive.

[obermeier]

Currently, a value change is detected if the value of a predefined attribute changes between two events.

Since it is possible to set the scope of an attribute as a dimension in the event schema, I like the idea of differentiating the state among these dimensions.
As it is done in the Datalake sink

What do you think of the idea of storing the state for each dimension (or for a fixed number)?

E.g.

In this example the attribute source has the property scope dimensional and this three events appear one after the other.

	{
          "source": "sensor1",
	  "state": 1
	}

	{ 
          "source": "sensor2",
	  "state": 2
	}
	
	{ 
          "source": "sensor1",
	  "state": 0
	}

This modification would result in a single state change when 'sensor1' switches from 1 to 0.

In the existing implementation, two state changes are detected because there is no differentiation between 'sensor1' and 'sensor2'.

[tenthe]

Hi,
I really like the idea for this new feature.
Cheers,
Philipp

[bossenti]

see #1673