feat : ajout d'un onglet formation

frontend/services/dto/formation.ts

@@ -0,0 +1,12 @@
+import type { Employee } from './employee'
+
+export type Formation = {
+  id: number
+  startDate: string
+  endDate: string
+  comment: string | null
+  justificatifPath: string | null
+  justificatifName: string | null
+  createdAt: string
+  employee?: Employee
+}