Fix types in Security example snippets

[bact]

Revise example snippets ("Syntax" section) in *VulnAssessmentRelationship classes:

• Put xsd:decimal value inside a quote
• Put CvssSeverityType entry value to lower case, per https://spdx.github.io/spdx-spec/v3.0/model/Security/Vocabularies/CvssSeverityType/
• Change to value to array (cardinality ..*) (in CvssV4VulnAssessmentRelationship)
• externalRefs -> externalRef
• externalIdentifiers -> externalIdentifier
• "externalIdentifierType": "securityAdvisory" -> "externalIdentifierType": "securityOther"
  • There is no securityAdvisory entry in ExternalIdentifierType vocab (It is in ExternalRefType vocab)
• Add security_ prefix to security properties
• @id -> spdxId
• @type -> type

[bact]

• See also #799