[AFP-91] ♻️ Modify 'ManagerService' (@asegers)

backend/order-management/src/main/java/com/afp/ordermanagement/service/ManagerService.java

 package com.afp.ordermanagement.service;
 
+import com.afp.ordermanagement.model.Manager;
+import com.afp.ordermanagement.repository.ManagerRepository;
+import com.google.api.client.googleapis.auth.oauth2.GoogleIdToken;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.stereotype.Service;
+import reactor.core.publisher.Flux;
+import reactor.core.publisher.Mono;
+
+import java.util.Optional;
+
+@Service
 public class ManagerService {
+    @Autowired
+    ManagerRepository managerRepository;
+
+    public Flux<Manager> getAll() {
+        return managerRepository.findAll();
+    }
+
+    public Mono<Manager> getById(String uuid) {
+        return managerRepository.findById(uuid);
+    }
+
+    public Mono<Manager> getByEmail(String email) {
+        return managerRepository.findByEmail(email);
+    }
+
+    public Mono<Manager> create(Manager newManager) {
+        return managerRepository.save(newManager);
+    }
+
+    public Mono<Manager> updateById(String uuid, Manager managerUpdates) {
+        return this.getById(uuid)
+                .map(existingManager -> Manager.combine(existingManager, managerUpdates))
+                .flatMap(managerRepository::save);
+    }
+
+    public Mono<Void> delete(Manager manager) {
+        return managerRepository.delete(manager);
+    }
 }