Add markers to barchart

**Why is this needed**: The user needs to be able to visualize a threshold for a single bar to see if a certain limit is reached. The current threshold system applies to all bars which can confuse the user if not all bars share the same limits. **What would you like to be added**: There should be an option for the user to add markers to a visualized field, based on input data. The markers should take the values of one field, and set a marker on a "target field" at those values. These markers should have options for shape and color to differentiate between them. It should be possible to add more than one marker per bar. **Who is this feature for?** Users who want to visually compare the value of a bar to the value of another input field. Think comparing things like current load vs max allowed load, where each bar has a distinct max load, making the current threshold system not a viable solution.