Create custom SSVC schema for CVE integration

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Note that the PR CVEProject/cve-schema#460 has been updated with a new script that is an node npm script at https://github.com/sei-vsarvepalli/cve-schema/blob/35c1d9ddb59e8446b2ed3251e14561da4f8dacb9/tools/ssvc_cve_schema.js
designed to modify the Schema with specific options to allow for CVE Program usage with their restrictions. Once it is adopted by the CVE Program, we will have to write a new schema that is specific to SSVC v2.0.0 for CVE program with these restrictions.

1. No target-ids in the SSVC v2.0.0 record
2. Namespace for SSVCv2.0.0 record restricted to enum("cisa", "cvss", "ssvc", "aivss")
3. No duplicate schemaVersion field in the SSVC v2.0.0 record

Originally posted by @sei-vsarvepalli in #681