Add support for textposition='middle left' to timelines and Bar objects

[rfeague]

Currently the label text for bar graphs (which are in turn used by timelines) can only be positioned inside or outside the box. For timelines, which are traditionally horizontal, the text is right-justified in the box, which is sometimes not desirable. It is pretty darn complex to figure out a way to change that justification! My feature request is that there should be a simple way to left-align the text in a timeline or horizontal bar graph.

[rfeague]

I truly spent hours researching this, only to find in the minutes after positing this that the text can be left-aligned by calling
fig.update_traces(insidetextanchor='start')