Add docstring to peripheral pipeline components

## Description of task

Add docstrings to document all parts of the following components.
 - diagnostics,
 - trace-archiver-hdf5 (possibly trace-archiver-tdengine),
 - trace-reader, and
 - trace-telemetry-exporter

All functions/methods/structs/enums/etc. should be documented to explain what they do and what failure modes are possible.
