Allow Sbom::Occurence.component_version to be nullable

What does this MR do and why?

Describe in detail what your merge request does and why.

.components[].version is an optional field in CycloneDX 1.4. Because of this, we need to account for the fact that the component version may not be present. This change allows for sbom_occurrences.component_version_id to be nullable, and instead requires that a component_id must be present. Previously, we would have fetched the component_id through the component_version relation. This allows us to continue to maintain a component list even if version information for the component is not available.

See #366194 (comment 1033145384) for more details.

These diagrams illustrate the change:

Before	After

Migrations

Up

main: == 20220726154013 AddComponentIdToSbomOccurrences: migrating ==================
main: -- add_column(:sbom_occurrences, :component_id, :bigint, {:null=>false})
main:    -> 0.0027s
main: == 20220726154013 AddComponentIdToSbomOccurrences: migrated (0.0035s) =========
main: == 20220726154014 AddIndexToSbomOccurrencesComponentId: migrating =============
main: -- transaction_open?()
main:    -> 0.0000s
main: -- index_exists?(:sbom_occurrences, :component_id, {:name=>"index_sbom_occurrences_on_component_id", :algorithm=>:concurrently})
main:    -> 0.0099s
main: -- execute("SET statement_timeout TO 0")
main:    -> 0.0006s
main: -- add_index(:sbom_occurrences, :component_id, {:name=>"index_sbom_occurrences_on_component_id", :algorithm=>:concurrently})
main:    -> 0.0022s
main: -- execute("RESET statement_timeout")
main:    -> 0.0006s
main: == 20220726154014 AddIndexToSbomOccurrencesComponentId: migrated (0.0263s) ====
main: == 20220726154015 AddComponentForeignKeyToSbomOccurrences: migrating ==========
main: -- transaction_open?()
main:    -> 0.0000s
main: -- foreign_keys(:sbom_occurrences)
main:    -> 0.0060s
main: -- transaction_open?()
main:    -> 0.0000s
main: -- execute("ALTER TABLE sbom_occurrences\nADD CONSTRAINT fk_d857c6edc1\nFOREIGN KEY (component_id)\nREFERENCES sbom_components (id)\nON DELETE CASCADE\nNOT VALID;\n")
main:    -> 0.0017s
main: -- execute("ALTER TABLE sbom_occurrences VALIDATE CONSTRAINT fk_d857c6edc1;")
main:    -> 0.0015s
main: == 20220726154015 AddComponentForeignKeyToSbomOccurrences: migrated (0.0143s) =
main: == 20220726154016 MakeComponentVersionNullable: migrating =====================
main: -- change_column_null(:sbom_occurrences, :component_version_id, true)
main:    -> 0.0012s
main: == 20220726154016 MakeComponentVersionNullable: migrated (0.0014s) ============

Down

$ scripts/db_tasks db:migrate:down VERSION=20220726154016
main: == 20220726154016 MakeComponentVersionNullable: reverting =====================
main: -- change_column_null(:sbom_occurrences, :component_version_id, false)
main:    -> 0.0035s
main: == 20220726154016 MakeComponentVersionNullable: reverted (0.0087s) ============
$ scripts/db_tasks db:migrate:down VERSION=20220726154015
main: == 20220726154015 AddComponentForeignKeyToSbomOccurrences: reverting ==========
main: -- transaction_open?()
main:    -> 0.0000s
main: -- remove_foreign_key(:sbom_occurrences, {:column=>:component_id})
main:    -> 0.0196s
main: == 20220726154015 AddComponentForeignKeyToSbomOccurrences: reverted (0.0329s) =
$ scripts/db_tasks db:migrate:down VERSION=20220726154014
main: == 20220726154014 AddIndexToSbomOccurrencesComponentId: reverting =============
main: -- transaction_open?()
main:    -> 0.0000s
main: -- indexes(:sbom_occurrences)
main:    -> 0.0105s
main: -- execute("SET statement_timeout TO 0")
main:    -> 0.0005s
main: -- remove_index(:sbom_occurrences, {:algorithm=>:concurrently, :name=>"index_sbom_occurrences_on_component_id"})
main:    -> 0.0016s
main: -- execute("RESET statement_timeout")
main:    -> 0.0005s
main: == 20220726154014 AddIndexToSbomOccurrencesComponentId: reverted (0.0246s) ====
$ scripts/db_tasks db:migrate:down VERSION=20220726154013
main: == 20220726154013 AddComponentIdToSbomOccurrences: reverting ==================
main: -- remove_column(:sbom_occurrences, :component_id)
main:    -> 0.0022s
main: == 20220726154013 AddComponentIdToSbomOccurrences: reverted (0.0029s) =========

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