GLOWS: allow manual reprocess of L3b+ (Phase D deferred)

[jtniehof]

Summary

In rare cases, the external dependencies to GLOWS L3b/L3c may change so dramatically that we need to reprocess L3b and later, downloading all the latest external inputs.

This may be supported by the SDC reprocessing endpoint, but need to check for any interactions with the weirdness of the initializer.

Requirements

• Ability to reprocess L3b+ for a particular CR using the latest external inputs
• Download all external inputs, no need to only update one
• Use latest L3a as well, no need to "use previous L3a and just update external"

Related tickets

#42, #44

Estimate

16 hours for the ability to trigger with a fake descriptor, plus additional SDC work to support pure manual runs in the dependency system.

A workaround exists now which would require no development time.

[jtniehof]

The time-based trigger in the SDC kicks off the initalizer, which just checks for possible new files to process. So we can't use the SDC reprocess endpoint to force this.

Two options:

1. Create a fake descriptor in the dependency system, which is a manual trigger only and triggers the initializer. Initializer interprets it as "force reprocess this CR". This would require support for pure manual runs in the SDC dependency system. The estimate is based on this approach.
2. Workaround: download an existing L3a, bump the version number, and upload it. This would involve more than just changing the filename, as there is version and filename metadata in the global attributes, but it would be fairly straightforward for something that we expect to be rare.