Docs - Combine chart theme examples with color for charts page

[edonehoo]

Follow-up to patternfly/patternfly-org#4412

Move the chart theme examples to the "colors for charts" page, since those guidelines also cover theming:
https://github.com/patternfly/patternfly-react/blob/main/packages/react-charts/src/victory/components/ChartTheme/examples/ChartTheme.md?plain=1