Overlapping labels, label alignment - add workaround to documentation

There are quite a few open issues (or closed but regressed issues) that have problems with labels.

I found the best way to paint a label and change its rotation was with a custom painter using code similar to this.

Thought I'd add the workaround here and link to the other issues and perhaps ask for an update to the documentation. Note, I couldn't seem to get the text to overlay and have a higher 'z index' to appear over the top of the bar charts so I'm just putting the description next to it.

```
return SideTitleWidget(
axisSide: AxisSide.left,
child: Container(
width: 10,
child: RotatedBox(
quarterTurns: 3,
child: CustomPaint(
painter: MyCustomPainter(text: text, textStyle: style),
),
),
),
);
```

```
class MyCustomPainter extends CustomPainter {
final String text;
final TextStyle textStyle;

MyCustomPainter({super.repaint, required this.textStyle, required this.text});

@override
void paint(Canvas canvas, Size size) {
const textStyle = TextStyle(
color: Colors.black,
fontSize: 20,
);

var textSpan = TextSpan(
text: text,
style: textStyle,
);
final textPainter = TextPainter(
text: textSpan,
textDirection: TextDirection.ltr,
);
textPainter.layout(
minWidth: 0,
);

final offset = Offset(15, 30);
textPainter.paint(canvas, offset);
}

@override
bool shouldRepaint(CustomPainter oldDelegate) {
return false;
}
}
```

#1132 #1434 #922 #911

Note: it isn't 'perfect' as the gridlines and anything else is painted on top of the labels.

Start by locating the documentation for labels and SideTitleWidget, then review the linked issues #1132, #1434, #922, and #911. Document the provided CustomPainter workaround and its limitation that gridlines and other elements can still paint over the labels; done means the workaround is discoverable in the relevant documentation.

Written by the indexing model from the issue text.