Canvas: Threshold value assigned to a variable

<!-- Please only use this template for submitting feature requests --> **Why is this needed**: For example, I have a series of canvas panels. These all have the same threshold values. To change this, each panel has to be changed.  **What would you like to be added**: If these thresholds were controlled by a variable, it would be very easy to change them. here is an example   This makes it possible to control threshold values dynamically. **Who is this feature for?** [Add information on what kind of user the feature is for.]