Add CVSSv4 crosswalk

[ahouseholder]

Some elements of CVSSv4 vectors have implications for interaction with Vultron states. We should map those out as a crosswalk similar to https://certcc.github.io/Vultron/reference/ssvc_crosswalk

[ahouseholder]

Following is what we had said about CVSS 3.1 in the State-based model paper

CVSS version 3.1
includes a few Temporal Metric variables that connect to this model.
Unfortunately, differences in abstraction between the models leaves a good
deal of ambiguity in the translation. The table below shows the
relationship between the two models.

States	CVSS v3.1 Temporal Metric	CVSS v3.1 Temporal Metric Value(s)
$\cdot\cdot\cdot\cdot XA$	Exploit Maturity	High (H), or Functional (F)
$\cdot\cdot\cdot\cdot X \cdot$	Exploit Maturity	High (H), Functional (F), or Proof-of-Concept (P)
$\cdot\cdot\cdot\cdot x \cdot$	Exploit Maturity	Unproven (U) or Not Defined (X)
$Vf\cdot\cdot\cdot\cdot$	Remediation Level	Not Defined (X), Unavailable (U), Workaround (W), or Temporary Fix (T)
$VF\cdot\cdot\cdot\cdot$	Remediation Level	Temporary Fix (T) or Official Fix (O)