Improve RadioButtonGroup doc

[glebfox]

Existing page: https://docs.jmix.io/jmix/flow-ui/vc/components/radioButtonGroup.html

1. Add example of itemsContainer usage in XML.

2. Add example of itemsEnum usage both XML and Java

3. Add Example of programmatic setting items: List, Map: https://demo.jmix.io/ui-samples/sample/radio-button-group-custom-items

4. Both itemsContainer and itemsEnum attributes refers to ComboBox component doc. Since this two component have no common base component, either move itemsContainer and itemsEnum description to common attributes page or add detailed description for the RadioButtonGroup

5. Add css, ariaLabel, ariaLabelBy common attributes

6. Add Style variants description and examples: See Vaadin doc

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CUBA Doc as an inspiration: https://doc.cuba-platform.com/manual-latest/gui_RadioButtonGroup.html