Change `vulnerabilities.finding_id` column to NOT NULL

...und_migrations/backfill_finding_id_in_vulnerabilities.yml

...nd_migrations/drop_vulnerabilities_without_finding_id.yml

..._migrate/20240214204757_finalize_finding_id_migrations.rb

db/post_migrate/20240214204805_make_finding_id_not_null.rb

db/schema_migrations/20240214204757

db/schema_migrations/20240214204805

db/structure.sql

ee/app/models/ee/vulnerability.rb

ee/app/models/vulnerabilities/finding.rb

ee/app/services/vulnerabilities/create_service.rb

ee/app/services/vulnerabilities/manually_create_service.rb

...vulnerabilities/starboard_vulnerability_create_service.rb

ee/spec/factories/vulnerabilities.rb

ee/spec/factories/vulnerabilities/identifiers.rb

...igration/fix_namespace_ids_of_vulnerability_reads_spec.rb

...d_migration/migrate_shared_vulnerability_scanners_spec.rb

...ties_feedback_to_vulnerabilities_state_transition_spec.rb

...b/background_migration/create_vulnerability_links_spec.rb

ee/spec/models/vulnerabilities/finding_spec.rb

...s/security/ingestion/tasks/ingest_vulnerabilities_spec.rb