Some improvements to HorizontalBarChartView

[boherna]

Improvements (based on my own needs):

• Supports custom text to show next to the bars (in my case I needed a different text than the default provided).
• Adjusts the height and size of the bars and circles, respectively, when the size of the dynamic font changes.
• Allows setting the max value for calculating the bar width (in my case I needed charts with different dataPoints to have a normalised width regardless of the max values of those dataPoints).

I also changed RoundedRectangle by Capsule to guarantee the rounded edges no matter the height of the bar.

Thanks for sharing SwiftUICharts!