Add list-providers command

[wagoodman]

Since the provider config generation from vunnel has been added, this ports over the daily data sync workflow to deriving the provider matrix from grype-db output (which runs vunnel internally), not a static grype-db config.

Additionally this PR:

• removes a very noisy slack notification in leu of a notification at the end of the data sync workflow
• fixes the makefile to always reference the publish config when running grype-db
• updates the aggregation script to use the make target
• allows for the daily db sync to continue on failure, using the previous day's cache for today's cache