feat(mui): add circular progress to <Show>

[issa012]

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What is the current behavior?

<Show isLoading={true}> in MUI doesn't show loading spinner

What is the new behavior?

Added loading spinner. fixes #5668

Notes for reviewers

Hello. This is my first PR ever. I have added the <Backdrop> along with <CircularProgress> to render a loading spinner. Should I add the possibility to pass props to these components? Also, what color should they be?

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[issa012]

Hello @aliemir . What tests should I add for this change? Similar Antd component does not have any tests regarding the loading state. Should I update the documentation?