LightDB Stream: fix heading and other formatting

[szczys]

• add support for JSON syntax highlighting
• Place headings for better readability
• Use H2 headings for top-level sections division
• Begin sections with text rather than bullet point
• Add json as type for code examples for proper syntax highlighting
• Update copy for readability

resolves https://github.com/golioth/devrel-issue-tracker/issues/48

[github-actions[bot]]

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