Add missing SNS example .rst files

[mjfxjas]

Summary

• add missing SNS command example files under awscli/examples/sns
• include examples for SMS sandbox, data protection policy retrieval, origination number listing, and batch publish

Testing

• docs/examples only change

Closes #10062

[mjfxjas]

Quick follow-up on this docs/examples PR.

I added the missing SNS example .rst files to close gaps in example coverage. Happy to rework file naming or location if there is a preferred convention I should follow.

[mjfxjas]

Thanks for flagging this overlap. I checked #10071 and it appears to cover the same SNS example files.\n\nTo avoid duplicate review effort, I am closing this PR in favor of #10071. If maintainers would prefer cherry-picking any wording from this branch, I can reopen and narrow to only non-overlapping changes.

[mjfxjas]

Closing as duplicate of #10071 to keep discussion and review in one place.