Add a shared gateway tracing demo with Mongoose

[udsmicrosoft]

Summary

• add a reusable local stack with the published tracing-enabled DocumentDB image, OpenTelemetry Collector, and Jaeger
• add optional Mongoose HTTP and client spans with W3C trace-context propagation into gateway requests
• validate query filters and restrict updates to supported book fields
• make custom host gateway ports work consistently across all playground readiness checks
• provide scripts that start the demo and verify a connected application-to-gateway trace

Validation

• pulled ghcr.io/documentdb/documentdb/documentdb-local:trace-4fbbfcb8 at manifest digest sha256:d02b04ad23c6474d0150c34e432e1d4cbcdf70a2b8c02ef86671bf925a02cd35
• deployed a clean DocumentDB, OpenTelemetry Collector 0.157.0, and Jaeger 2.20.0 stack
• verified the trace hierarchy GET /stats/genres -> mongoose.aggregate -> gateway.request -> gateway.process_request -> postgres.execute
• passed all 16 Mongoose compatibility checks
• verified invalid query and update payloads are rejected while supported updates succeed
• passed CodeQL, shell syntax, Node syntax, Compose configuration, and diff whitespace checks