Second docs slice shipped alongside the webhook listener code so users
can actually wire up the endpoint the moment this PR lands.
- website/docs/user-guide/messaging/msgraph-webhook.md: new page
covering what the listener is (change-notification ingress, distinct
from the teams chat adapter), quick-start YAML + env-var config,
full config table, security hardening (clientState + timing-safe
compare, source-IP allowlisting against Microsoft's published egress
ranges, TLS termination at the reverse proxy, response hygiene),
status-code table, troubleshooting, and cross-links to the Azure
app registration guide.
- website/docs/reference/environment-variables.md: new Microsoft
Graph Webhook Listener subsection with MSGRAPH_WEBHOOK_ENABLED,
_PORT, _CLIENT_STATE, _ACCEPTED_RESOURCES, _ALLOWED_SOURCE_CIDRS.
- website/sidebars.ts: wire the new page into Messaging Platforms,
right after the teams chat adapter so the two related pages are
adjacent in the sidebar.
The pipeline runtime / operator CLI / outbound delivery pages still
land with their matching PRs. With this PR merged, an operator can get
the listener running end-to-end, register a Graph subscription
manually, and receive validation handshake plus notification POSTs
against the configured client_state.
Verified via npm run build: new page routes at
/docs/user-guide/messaging/msgraph-webhook, sidebar wires correctly,
no new warnings or errors.
