Create one tag rule.

Body: { projectId, conditions: [{ category, values: [{ value } | { personId }] }], thenCategory, thenValue?, thenPersonId?, applyToExisting? } Condition groups are ANDed; values inside a group are ORed. A category is 'person' (values carry personId) or a custom tag category of the project (values carry value). applyToExisting=true also applies this rule to the photos already in the project; otherwise it only applies from now on. Returns { rule, appliedToImages }.