Add sync worker for advisories

What does this MR do and why?

Adds worker for importing advisory package metadata.

Notable changes:

• Worker
  • Renames existing sync worker to licenses
  • Adds worker for advisories similar to above
  • Extract stop signal into its own class and allow sync service to instantiate it
  • ExclusiveLease passed to sync service
• Sync Service
  • Add advisories support
  • Instantiate stop signal in class method
  • Better logging of sync position
    • Invoke self-describing #to_s on BaseDataFile and SyncConfig
  • Call stubbed advisory ingestion service (being added in Ingest advisory and affected package data to DB (!123149 - merged))
• Sync Config
  • Check whether old offline path is available for licenses
• Feature flag to control ingestio

Changelog: added

How to set up and validate locally

See here.

Or:

1. bundle exec rails console
2. ENV['PM_SYNC_IN_DEV'] = 'true'
3. ::License.feature_available?(:dependency_scanning) should evaluate to true
4. PackageMetadata::AdvisoriesSyncWorker.new.perform should generate calls to gcp bucket and error out with NoMethodError from AdvisoryIngestionService since it is being added in !123149 (merged)

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #370780 (closed)