[ENHANCEMENT] Add Data Values

[steve257]

Ability to add data values onto chart for first and last data points of line

Display Options: No Values, First & Last Values, Last Values Only
Position Options: Above Data Value, Below Data Value, Adjacjent to Data Value Left/Right

Eg:
https://miro.medium.com/max/2800/1*BCt_FPXhkPpjDr1wAakSww.png
https://miro.medium.com/max/2800/1*HvoXEtGQuMS0ZVvNayKk0w.png

[dm-p]

I spent a lot of time researching this and other analytics features while developing the current version and I can't do it in a maintainable way because custom visuals don't seem to fully support container IDs (measure selection) yet.

I have a lot of code written already but have put it on hold until the team can resolve or advise on microsoft/PowerBI-visuals-tools#283 or the email I've already sent asking for support on this particular issue. I've followed this up to see if there's been any traction since I last asked.

I've worked around it for the line styling by adding a divider (---) between each measure in the properties pane but when I started working on data labels, the number of properties and potential data points to manage got way too unwieldy and resulted in horrible UX.