feat: add dynamic data label position option for bar charts in Insights

[Raghav0201]

Summary

This PR adds a new Label Position option for bar chart data labels in Insights.
Users can now choose where data labels appear: Top, Center, or Bottom.

Why this is needed

Earlier, Insights had limited control over data label placement.
For dense bar charts, labels often overlap or are difficult to read.
This enhancement improves readability and restores a previously available feature.

What’s added

• New label_position field in Y-Axis configuration
• UI dropdown to choose label position (Top / Center / Bottom)
• Respect user-selected position for bar charts
• Line charts continue to use top by default
• Fully compatible with:
  • stacked bars
  • swapped axis charts
  • normalized charts

How it works

• The selected label_position is stored in y_axis.label_position
• helpers.ts reads this value and applies it to all bar series
• Line series ignore this setting (as expected)

Testing done

• Tested in local bench build
• Verified with dashboard widgets
• Checked with multiple series, stacked bars, and split-by charts

Screenshots

• Chart View

• When the user enables “Show Data Labels”, a new dropdown called “Label Position” becomes visible.

• User can select Top / Center / Bottom

• Center Label View

• Bottom Label View