feat(policy)!: undo subject mapping operator decomposition

The operator decomposition split SubjectMappingOperatorEnum into
ConditionComparisonOperatorEnum + ConditionQuantifierEnum (+ case_insensitive)
and rewired DynamicValueResolver onto the comparison enum. The decomposed
evaluator was never adopted on main, so the added surface is unused complexity.

Undo the decomposition while keeping the DynamicValueMapping feature:

- Remove ConditionComparisonOperatorEnum and ConditionQuantifierEnum.
- Remove the comparison, quantifier, and case_insensitive fields from Condition
  and restore Condition.operator to required.
- DynamicValueResolver now uses SubjectMappingOperatorEnum. NOT_IN is rejected at
  the buf.validate boundary because dynamic resolution is existential.
- Drop case_insensitive everywhere.
- Remove the Comparison*/Quantifier* shorthand consts and regenerate protocol/go
  and the policy docs.

BREAKING CHANGE: ConditionComparisonOperatorEnum and ConditionQuantifierEnum are
removed; Condition.comparison/quantifier/case_insensitive are removed and
operator is required again; DynamicValueResolver.comparison is replaced by
operator (SubjectMappingOperatorEnum).

Signed-off-by: Krish Suchak <suchak.krish@gmail.com>

Author: alkalescent