Add missing STT and Telemetry domain overview files

[Coldaine]

The stt and elemetry domains currently lack overview files required by MasterDocumentationPlaybook 1.0.1 (4.1).

• Create docs/domains/stt/stt-overview.md.
• Create docs/domains/telemetry/tele-overview.md.
• Ensure they contain the domain_code frontmatter.

[google-labs-jules]

Jules is on it. When finished, you will see another comment and be able to review a PR.

[google-labs-jules]

Ready for a review! A PR has been created.