Document push builder usage and new push type 102

[shai-almog]

Summary

• document push type 102 and add an example payload walkthrough
• show how to use PushBuilder for rich notifications and client-to-client pushes
• explain how to retrieve metadata, titles, actions, and text replies from PushContent

Testing

• not run (documentation only)

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https://chatgpt.com/codex/tasks/task_e_68fb17bbd830833191e71f0a4c8f49e7

[github-actions]

Developer Guide build artifacts are available for download from this workflow run:

• Developer Guide HTML package
• Developer Guide PDF
• AsciiDoc linter report
• Vale report
• Unused image report

Developer Guide quality checks:

• AsciiDoc linter: No issues found (report)
• Vale: 18586 alert(s) (2730 errors, 6296 warnings, 9560 suggestions) (exit code 1) (report)
• Image references: No unused images detected (report)