Switch to SSVC v2

[tschmidtb51]

Currently, we are on SSVC v1 but the most current one is SSVC v2 - we need to make the switch right now to solve some issues.

[tschmidtb51]

Related issues:

• Use extension instead of private for SSVC namspaces #985
• Unclear specification of registered SSVC roles #1021
• Increase test coverage for mandatory test 6.1.47 #1076
• 6.3.12: Clarify relationship CVSS vs. SSVC #1053 => add a test here

[tschmidtb51]

Todos:

• update schema
• update referenced schemas
• update test scripts
• update prose
  • links
  • metrics
  • introduction
  • guidance on size
• tests
  • 6.1.46
  • 6.1.47
  • 6.1.48
  • 6.1.49
  • 6.2.34
  • 6.2.35
  • 6.2.36
  • 6.2.37
  • 6.3.13
  • 6.3.14
  • 6.3.15
  • [ ] 6.3.12 (add test file): striked off the list to avoid unnecessary merge conflicts. If important, can be done later
• add test preset

[tschmidtb51]

Open:

• update registered namespaces
• check invalid example (6.1.48-21) - reserved in Reserve registered namespace invalid CERTCC/SSVC#907