[tlBMC/g3doc] Document Sensor Collector

Created documentation for the Sensor Collector and Aggregator in `components/collectors/sensor_collector.md`.
Details its purpose, sensor instantiation, read scheduling, data handling, concurrency, dynamic configuration, and dependencies.
Based on `collector/sensor_collector.cc` and `collector/sensor_collector_aggregator.cc`.

PiperOrigin-RevId: 930707666
Change-Id: Ifd0832421109246f5cea4deac946583103d03a43