[Docs cleanup] Retire x-ms-* extension authoring docs

[lirenhe]

Context: x-ms-* extensions are now produced by the TypeSpec emitter rather than hand-added to Swagger.
The docs that teach hand-authoring these extensions should be converted to TypeSpec guidance or archived.

Tasks:

• 🟡 documentation/x-ms-examples.md — convert to TypeSpec example guidance, or archive
• 🟡 documentation/x-ms-pageable/example1.yaml — archive as legacy Swagger sample (or convert to TypeSpec)
• 🟡 documentation/x-ms-pageable/example2.yaml — archive as legacy Swagger sample (or convert to TypeSpec)
• 🟡 documentation/x-ms-pageable/example3.yaml — archive as legacy Swagger sample (or convert to TypeSpec)