Button - Move icon children to the icon prop

[wise-king-sullyman]

Follow up to breaking change PR patternfly/patternfly-react#10663 and to help with patternfly/patternfly-react#10698

In the empty state codemod I was able to identify icon children and move those to the icon prop, we should do that for buttons as well rather than only moving icons for plain buttons.

Required actions:

1. Build codemod
2. Build test
3. Update readme with description & example