docs(jaas): document overriding TURN relay to a specific region [JIT-16146]

[aaronkvanmeerten]

Summary

Adds a JaaS developer-docs FAQ entry documenting how embedders can pin the TURN relay to a specific region using the experimental iceServers option of the JitsiMeetExternalAPI iFrame API.

This is distinct from region-pinning the media bridge (JVB) via the *.8x8.vc regional domains (already documented) — this covers the separate TURN relay media path used when a participant cannot reach the bridge directly.

Changes

• New FAQ entry "Can we restrict the TURN relay to a specific region?" in docs/jaas/docs/faq.md.
• Working iceServers.replace example pinning turn/turns to prod-8x8-eu-central-1-turnrelay-oracle.jitsi.net (EU-Central-1 example).
• Table of the 10 regional relay hostnames.
• Note that the option is experimental, iframe-only, and that JaaS continues to issue the short-lived TURN credentials (only the relay host is overridden).

Notes for reviewers

• Please confirm the relay port/transport advertised by the coturn relays — the example uses :443?transport=udp (turn) and :443?transport=tcp (turns); adjust if incorrect.
• The relay table includes Canada (Central) and Middle East (Bahrain), which are not in the existing "Where do you have data centers?" list; may be worth reconciling.

Ticket

JIT-16146 — https://agile.8x8.com/browse/JIT-16146