Sharing groups

[tschmidtb51]

• resolves https://github.com/oasis-tcs/csaf/issues/705
• add sharing_group to JSON schema
• adapt prose to reflect sharing group changes
• add RFC 9562 to normative references
• add RFC 4122 to informative references
• add mandatory test to prevent usage of Max UUID in other TLP than CLEAR (6.1.39)
• add mandatory test to prevent usage other UUID than Max UUID in TLP:CLEAR (6.1.40)
• add mandatory test to prevent usage of reserved names (6.1.41)
• add mandatory test to enforce usage of sharing group names (6.1.42)
• add rule about the relationship between sharing group ID and /document/tracking/id
• add optional test to discourage usage of Max UUID (6.2.28)
• add optional test to discourage usage of Nil UUID (6.2.29)
• add optional test to discourage usage sharing group with TLP:CLEAR (6.2.30)
• add invalid examples
• add valid examples
• adapt testcases list and schema
• add suggestions for quick fixes throughout the sharing group tests
• add guidance of size for UUIDs
• swap date and URI to make it alphabetic amongst the "special" strings
• convert headings into title case

[tschmidtb51]

Pending motion: https://groups.oasis-open.org/discussion/motion-for-826

[santosomar]

Dear CSAF TC Members,

The motion to accept the changes described in pull request as suggested in https://github.com/oasis-tcs/csaf/pull/826 and include it into CSAF 2.1 has passed.