Add RFC for guided Cosmos DB Emulator local experience

[Sajeetharan (sajeetharan)]

Summary

• propose a guided Docker-based Azure Cosmos DB Emulator setup flow under Local Emulators
• define image, persistence, readiness, ownership, rollback, reconciliation, security, accessibility, and telemetry requirements
• preserve the existing manual New Emulator Connection... workflow for externally managed emulators

Tracks #3285.

Validation

• npm run prettier
• verified balanced Markdown fences, unique section headings, and contiguous FR-1 through FR-25 requirements
• verified the RFC image, ports, persistence paths, readiness probe, endpoint discovery, and scoped TLS requirements against docker-compose.yml and test/e2e/setup/emulator.ts

Known validation issue

• npm run lint currently fails on pre-existing TypeScript safety errors in account overview and throughput code; this PR adds only Markdown

[github-actions]

✅ Build (Compile, Lint, Prettier, l10n, Package)

🧱 Step Results

• Validate Version: ✅ success
• Localization: ✅ success
• Lint: ✅ success
• Prettier: ✅ success
• Compile (tsc): ✅ success
• Package: ✅ success
• External Skills (info): ✅ success

📥 Artifacts (run)

• feature-cosmosdb-emulator-local-rfc-0.37.0-1e1053d — 3.68 MB

[github-code-quality]

Code Coverage Overview

Languages: TypeScript

TypeScript / code-coverage/vitest

The overall coverage in commit 2b6bb1a in the feature/cosmosdb-emu... branch remains at 76%, unchanged from commit 2e8b478 in the main branch.

[github-actions]

🧪 Tests (Unit + Integration)

🧪 Results

• Unit Tests (vitest): ✅ success
• Integration Tests (extension host): ✅ success

📈 Coverage

• Download HTML report