Add explicit Agent365 baggage bridge

[heyitsaamir]

Adds the explicit Agent365 baggage bridge and documents the app-level Microsoft OTel setup around it.

Why

Agent365 observability should be wired by the app, not hidden inside generic Teams SDK telemetry. This keeps the SDK boundary tidy: Teams.py emits SDK spans/metrics and provides an opt-in Agent365 baggage bridge; app code owns Microsoft OpenTelemetry setup, token auth, exporters, and Agent365 scopes. Almost suspiciously reasonable.

Interesting bits

• Adds agent365_baggage(...) and Agent365Baggage as the explicit context-manager bridge.
• Uses only standard OpenTelemetry API baggage/context in SDK code; no microsoft-opentelemetry or Microsoft Agents SDK dependency in SDK packages.
• Maps conservative Agent365 correlation context from Teams activity by default: tenant, conversation, channel, agent/app identity, user ID, and optional invoke-agent server details.
• Keeps message content, attachments, names, and emails out of baggage by default; display identity details require an explicit opt-in.
• Updates Agent365 docs with app-level Microsoft OTel setup, explicit baggage usage, resolver/auth guidance, and content/output logging left off by default.

Reviewer tips

Start with the small bridge in Apps diagnostics, then the tests that prove it is opt-in and dependency-free. The README is the contract for how app code combines agent365_baggage(...) with Microsoft OTel/Agent365 scopes.

Testing

Targeted Apps diagnostics/process tests pass locally. CI will rerun for the updated branch.

[corinagum]

Same feedback as TS