Remediation categories

[tschmidtb51]

• addresses parts of https://github.com/oasis-tcs/csaf/issues/563, https://github.com/oasis-tcs/csaf/issues/662
• add values optional_patch and fix_planned as remediation category
• adapt prose
• add conversion rules from CVRF
• add conversion rules from CSAF 2.0
• restructure mutually exclusive categories
• clarify that reference of products can be direct or indirect
• add mandatory test for contradicting remediations
• add mandatory test for contradicting Product status remediations combinations
• add optional test for discouraged product status remediation combinations
• add invalid examples
• add valid examples
• add table for contradicting product status group remediation category combinations

[tschmidtb51]

Due to recreation of the branch superseded by #807.