Fix manifest file hierarchy search order

Checklist

• documentation is changed or added in ./docs
• unit tests updated to test changes

Description

Context

While working on the experimental RPM collector plugin, it was observed that repositories in parent manifest weren't being consistently propagated to child manifest(s) as expected.

Intent

• Add repositories field validator to Manifest model
• Move generation of component search sequence data from sboms field validator into new repositories validator
  • Reorder fields in ManifestFile model (the superclass of Manifest) so that the sboms field is validated before the repositories field
  • This ensures that the sboms data is already available during validation of the repositories field
• Refactor to extract component search sequence logic into new _add_repository_search_sequence method