Padding for text label of extralines

Hello and thank u for great chart library!

It would be nice to have padding around text, because for now for make text look nicer we have to use spaces on both sides of text.

**Example (with padding):**

**Example (how it works now):**

THank you for your help!

Start by locating the extralines text-label rendering and its existing label configuration in the Flutter chart library. Compare the two screenshots and determine how padding should be exposed; the work is done when labels can have visual padding without adding spaces to their text.

Written by the indexing model from the issue text.