Outdated documentation still using legacy annotation model

[fmbenhassine]

The section that documents how to group commands still uses the legacy annotation model. It should be updated to use the new annotation model.

The same applies to the exception resolution section.

Same thing in other places as well:

https://docs.spring.io/spring-shell/reference/commands/interactionmode.html

https://docs.spring.io/spring-shell/reference/commands/writing.html

https://docs.spring.io/spring-shell/reference/completion.html

https://docs.spring.io/spring-shell/reference/components/ui/render.html

https://docs.spring.io/spring-shell/reference/execution.html

[zonk911]

Here as well
https://github.com/spring-projects/spring-shell/
readme.md still shows the old annotation model