filewriter: journals #86

The file-writing infrastructure must be able to write entries into the instrument journal.xml (and into the instrument journal MySQL database, journal_<inst> MS teams channels, and various other 'journal' workflows)

This is intentionally phrased as

file-writing infrastructure

as this may not belong in the filewriter itself, but in a separate cooperating process.

See also #11

Potential differences from existing files

Not all fields in the current journal.xml make sense in the streaming system, for example:

• icp_version; this could be populated with a filewriter version instead.
• detector_table_file does not exist in the streaming system. Suggest populating this entry with UNSPECIFIED or similar.
• spectra_table_file / wiring_table_file do not have the same meanings/formats/locations in the streaming system. Programs which expect to be able to read a specific format from the filepaths in these entries will fail.