Enable segmenting a line chart by a dimension

[hjkmarshall]

Description

• Currently, we support multi-line line charts derived from multiple metrics and a single data dimension.
• Users should be able to also create a multi-line line chart from a single metric and 2 dimensions.

Acceptance Criteria

• Create a new line chart option called 'Segmented line chart', that lets users select a single metric + a date dimension (for the x-axis) + an additional dimension to segment the data.
• It should show multiple lines representing each value in the dataset for the dimension being used to segment the data (just like the existing Stacked Bar or Stacked Area charts).
• Rename the existing line chart 'multi-metric line chart'.
• The new chart should use as much logic from the existing line chart as possible. If possible, point the new component to the existing line-chart.