Zoom level for the map separate from the aggregation level of the sites.

[dantravers]

Allows users to look at site-level forecasts but still zoom out to see a larger area of the UK, without the sites automatically aggregating up to the next zoom level (GSP, then DNO level).

Would involve having a separate aggregation level indicator on the map, with 4 levels: National, Region, Grid Supply Point, Site.

The user can select the level of aggregation on this widget, and zoom and pan separately on the map using the mouse wheel, pinch, etc.

A nicer way to allow the user to do this might be if initially the zoom of the mouse is automatically locked together with the aggregation level (as the current design is), but then if the user clicks on the widget to select the aggregation level, then it stays at that level until it is moved by the user to another level (or "unlocked" somehow?)

[braddf]

The aggregation/zoom functionalities are still coupled as of time of writing, so this would still be a relevant enhancement to add