add code examples

docs/site/docs/consumer-clients.md

docs/site/docs/getting-started.mdx

docs/site/plugins/webpackconf/src/index.js

docs/site/src/pages/styles.module.css

docs/site/src/theme/CodeBlock.tsx

examples/for_site/getting_started/c/consume.c

examples/for_site/getting_started/cleanup.sh

examples/for_site/getting_started/cpp/CMakeLists.txt

examples/for_site/getting_started/cpp/consume.cpp

examples/for_site/getting_started/cpp/produce.cpp

examples/for_site/getting_started/python/consume.py

examples/for_site/getting_started/python/produce.py