Multi-location: scaffold for job execution framework

[candu]

Description

554 and #555 form the basis for implementing scheduler on top of pg-boss (or, if needed, other tools). This task starts the actual implementation by creating a hierarchy of job-type-specific executor classes, and by integrating pg-boss within JobController.

Acceptance Criteria

• [x] create new class BackgroundJobBase, and create a new class BackgroundJobTest that extends it;
• [x] create a job metadata table in public to store progress stats, links, etc., and that refers to job IDs as well as user IDs;
• [x] create JobMetadataDAO with CRUD methods on this table;
• [x] write DAO tests for JobMetadataDAO methods in JobMetadataDAO.spec.js;
• [x] implement JobController endpoints:
  • [x] in create endpoint, create a new pg-boss job with given data and a new JobMetadata record that links to it;
  • [x] in cancel endpoint, cancel the pg-boss job by job ID;
  • [x] in status-checking endpoint, fetch both pg-boss job and JobMetadata record by job ID;
• [x] implement stub version of BackgroundJobGenerateReport:
  • [x] receives a list of (type, id, format) tuples;
  • [x] for each such tuple, logs that tuple out;
  • [x] for each such tuple, updates the JobMetadata record to reflect progress;
  • [x] once all such tuples have been written, returns a result containing a dummy ZIP file path.

Additional Notes Note that pg-boss initialization will need to be integrated with test:db-startup scripts at this point - totally doable, and should build off similar parts of #555 .

[candu]

Hit a couple of midsize challenges here.

First was authentication: to relate jobs to users, scheduler needed to share user sessions with web, which meant moving that out of its in-memory store in web and into database.

Second was timestamp handling: pg-boss uses TIMESTAMP WITH TIME ZONE columns, whereas MOVE uses TIMESTAMP WITHOUT TIME ZONE with the convention that all timestamps are jurisdiction-local. This meant adding a new set of types and validators to handle pg-boss timestamps.

Total impact here was roughly a day of work - though the tasks here did take into account a bit of unexpected additional time, so this isn't problematic by any means.