[Docs cleanup] Update SDK automation docs to TypeSpec + spec-gen-sdk

[lirenhe]

Context: SDK automation now flows through TypeSpec emitters + the spec-gen-sdk pipeline; the legacy
swagger-to-sdk / AutoRest paths should be removed from the docs.

Legend: 🔴 OBSOLETE (delete/archive) · 🟡 NEEDS-UPDATE (reword)

Tasks:

• 🟡 documentation/sdkautomation/README.md — remove swagger-to-sdk/AutoRest paths; document TypeSpec + spec-gen-sdk only
• 🟢 documentation/release-request/rules-for-release-request.md — keep (pointer to official release docs)