KAFKA-20366: Add syntax highlighting across docs (security and streams)

[gomudayya]

• Added syntax highlighting to code blocks in the Security and Streams sections.
• Updated authentication-using-sasl.md by adding line-continuation characters and refining indentation for better readability.
• Built kafka-site locally to verify the changes and manually checked each affected page.
• This is a follow-up PR to previous work (KAFKA-20050: Add syntax highlighting for code blocks and commands #21845, KAFKA-20366: Add syntax highlighting across docs, excluding security and streams #21887). With this change, the syntax highlighting across all relevant documentation pages is now completed.