* Add "When to use" info to Checkbox.mdx

Added info about how checkboxes generally work and when to use another component instead.

* Replaced words with proper component names

* Update Checkbox.mdx

Elaborate on explanations. Add examples for how to use checkboxes the user-friendliest way.

* Apply suggestions from code review

Co-authored-by: Dominik Prokop <dominik.prokop@grafana.com>

Co-authored-by: Tobias Skarhed <tobias.skarhed@gmail.com>
Co-authored-by: Tobias Skarhed <1438972+tskarhed@users.noreply.github.com>
Co-authored-by: Dominik Prokop <dominik.prokop@grafana.com>