Fix errors/nits in api-concepts

Nits fixed include:

- incorrectly specified code syntax, e.g. code snippet marked 'json' but
  the content is not JSON;
- the footnote in the paging table contains a nested table which cannot
  be rendered correctly, so the content is removed considering that it
  is just redundant table rows;
- some `kubectl apply` commands failed to provide the correct artifact
  to use while the artifact is stored online.
- fixed some other code fences by explicitly marking them as code
  snippet rather than relying on indentation (hard to maintain).

Author: tengqm