Add rankKey support to certification forms and exams

- Introduced rankKey field in Certification interface and payloads.
- Updated CertificationForm to handle rankKey input.
- Enhanced ScheduleExamModal to filter exams based on rank.
- Added getEligibleExams API query to fetch exams relevant to the application's rank.
- Updated related components and types to accommodate new rankKey functionality.

apps/backoffice/src/app/features/certificate-requirements/components/DocumentRequirementEditorDrawer.tsx

@@ -167,7 +167,7 @@ export function DocumentRequirementEditorDrawer({
           <>
             <Divider label={t('certReq.condition.title', 'Condition')} labelPosition="left" />
             <ConditionBuilder
-              value={(draft.conditionExpression ?? null) as ConditionValue | null}
+              value={(draft.conditionExpression ?? { field: '', equals: '' }) as ConditionValue}
               onChange={(v) => setDraft((d) => ({ ...d, conditionExpression: v ?? undefined }))}
               targets={conditionTargets}
               palette={palette}