Improve measurements chart

[rolandgeider]

See parent issue wger-project/wger#2417 for context

What to do

We need to display charts depending on the m data type, e.g. the type (a histogram for steps/sleep, two series for blood pressure, etc.).

The server exposes metric_type + aggregation on the category API and the client picks the representation from those (with line being the default and the current implementation).

metric_type	aggregation	chart
blood_pressure	paired (systolic/diastolic)	two series / range band
heart_rate	min/max/avg per day	range
steps, distance, energy, water	sum per day	bar / histogram
sleep	sum per day	bar
custom (default), weight, body_fat, height, blood_glucose, …	sample	line (unchanged)

• Cumulative metrics (aggregation=sum) are aggregated per day and shown as
  bars/histogram, not as raw sample points.
• Grouped categories (e.g. blood pressure) render their series together in one chart.
• Use the implementation in Added exponentially smoothed trendline for weight #1196 for the line char