[FR] be able to filter which X points to graph for an entity

[EzioArmando]

Please describe the idea

It would be nice, to be able -- for each entity being graphed -- to filter X-axis ranges, showing the entity's data points only in the filtered range

This could be implemented using:
a) min X and max X points; only points between the 2 would be graphed, or
b) as a formula that returns a boolean that is dynamically calculated for each X value to decide whether to graph the point or not

Some possible uses include:

1. to combine actual and forecast data: e.g. for past data, show the actual solar production till now (this part does not need filtering, as there's no future data) and in the same graph show forecast solar production from now (without showing the forecast values before now, which are useless)
2. to show time-range specific limits: e.g. a cap of 8kW during high-cost electricity hours and 12kW during low cost hours
3. to show an entity only when it exceeds a threshold: e.g. show the electrical consumption only if it exceeds 8kW; this would require #b above

All of the above can be done creating template entities, but is repetitive and not user-friendly, and needs to be maintained.

This feature request does not seem not be terribly difficult to implement.

The concept is explained for line charts, but could be extended to other graph types.