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

[josefaidt]

Is your feature request related to a problem? Please describe.
A clear and concise description of what the problem is. Ex. I'm always frustrated when [...]

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

Describe the solution you'd like
A clear and concise description of what you want to happen.

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

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

Additional context
Add any other context or screenshots about the feature request here.

[mauerbac]

cc @rachelnabors