Upgrades to SSVC 2.0.0

[sei-vsarvepalli]

This is an update to SSVC metrics with SSVC 2.0.0 included to support the newer schema's ability to provide contextual information for SSVC metrics. The changes are

1. Optional CVE ID's in the Selection Schema - so no need to duplicate CVE ID in the metric section
2. Add Namespace capabilities to provide specific and custom decision points as described by the publisher
3. Add options References and Decision Tree Resources to be associated to a published metric so there is clarity of SSVC metrics provided
4. Require Selection to be array of objects that can be iterated with key or value so the data can be minimized if preferred
5. Timestamp field to allow for Timezone if preferred and still have IETF RFC 3339 fidelity.