[Lens] Reference lines: improve decoration styling

[dej611]

Describe the feature:

Improve the way the reference lines are decorated with text:

What about moving the text inside the chart, above/below the line?

For horizontal line it definitely improves the readability of the text
For the vertical line, you can let the user choose the text direction (horizontal/vertical)
And you can keep the icon outside if you need that

Also centering the text is not always the perfect choice: if you are defining a vertical threshold, the text could be left-aligned to the line to specify that "everything gt this line has is above the threshold"

Follow up from #112921 (comment)

[dej611]

In order to provide better transparency of priorities, issues that will not be prioritized within the next 24 months are being closed.