feat(legacy-plugin-chart-country-map): added support for Legend options

[RoBYCoNTe]

SUMMARY

Country map seems to be not very clear when you have to see and check why specific color has been chosen for an area of the map. I think legend option is mandatory to improve readability of charts.

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

Before was not possible to configure legend, now you can use specific parameters to obtain it:

I've added few new config props:

• LEGEND: allow to set position of the legend (None, Top, TopLeft, TopRight, Bottom, BottomLeft, BottomRight)
• ORIENTATION: vertical or horizontal (like a color gradient)
• FONT SIZE: used to render each step of the legend.

TESTING INSTRUCTIONS

Run the application and create a new chart of type Country Map, you will see new parameters that can be used to customize visualization of the chart.

ADDITIONAL INFORMATION

• [ ] Has associated issue:
• [ ] Required feature flags:
• [x] Changes UI
• [ ] Includes DB Migration (follow approval process in SIP-59)
  • [ ] Migration is atomic, supports rollback & is backwards-compatible
  • [ ] Confirm DB migration upgrade and downgrade tested
  • [ ] Runtime estimates and downtime expectations provided
• [x] Introduces new feature or API
• [ ] Removes existing feature or API