Add `azdext.WaitForDebugger` to extensions for improved debugging

[JeffreyCA]

Implement azdext.WaitForDebugger functionality in first-party extensions so that all custom extension subcommands (not just core commands) can pause and wait for debugger when the AZD_EXT_DEBUG environment variable is set.

Details:

• All extension subcommands should support waiting for the debugger according to the pattern introduced in PR #6537, which adds a unified prompt behavior and robust handling for Ctrl+C or "No" answers.
• This improvement depends on the code and changes merged in #6537 (core wait-for-debug support and prompt behavior rewrite).

Acceptance:

• All custom subcommands of these extensions wait for debugger consistently
• Debugger waiting is controllable via AZD_EXT_DEBUG
• (Bonus) Extension docs and README updated to mention new debugging flow

Related context and previous work:

• Debugger/unified prompt in PR #6537
• Extension tracing and metadata sharing in #6496, #6528