MongoDB watcher, joined observations, geospatial values and metrics

[woksin]

Arc for TypeScript 0.26.0 closes most of the remaining gaps in the MongoDB integration. npm publication remains disabled, and full .NET parity is not yet available.

Added

• mongoDBWatcher observes changes to a tenant's collections as RxJS observables for application code, the counterpart of .NET's IMongoDBWatcher.
• Joined observations re-emit a primary collection's results when it or one or two related collections change, like .NET's joined observe builder.
• Fundamentals Point, LineString and Polygon values are stored as GeoJSON.
• MongoDB client metrics through OpenTelemetry for clients Arc creates.
• Reads retry transient MongoDB errors, at most twice.