styleguide suggestion: fenced code blocks should be succinct, contain necessary imports

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When reading the documentation and encountering code samples, it would be nice if we are able to copy and paste these samples into a file without issue. In short we should aim for:

- consistency
- copy/paste-ability

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Add a section to the styleguide to enforce the following for fenced code blocks:

- code blocks should use consistent code style
- naming convention of variables
- use of whitespace (e.g. JavaScript imports should be followed by a newline)
- code blocks in the same page/space should be consistent in use of imports (e.g. using `graphqlOperation`)
- code blocks should contain all imports necessary (i.e. if the sample contains usage of `API`, sample should also include the `API` import statement)
- code blocks should contain a sample filename
- when using relative imports we should provide a sample filename based on the project defaults (e.g. include `// src/App.jsx` where we aim to import the sibling `./aws-exports`
- code blocks should be formatted with the prettier config from this repo

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