Refactor deleteGroup method and add getUsersInGroup method

This commit refactors the `deleteGroup` method in the `BlurtingService` class to use the `getUsersInGroup` method instead of `getGroupUsers`. Additionally, a new method `getUsersInGroup` is added to the `UserService` class to retrieve users belonging to a specific group.

src/blurting/blurting.service.ts

@@ -184,7 +184,7 @@ export class BlurtingService {
   }
 
   async deleteGroup(group: BlurtingGroupEntity) {
-    const users = await this.userService.getGroupUsers(group.id);
+    const users = await this.userService.getUsersInGroup(group.id);
     for (const user of users) {
       user.group = null;
     }

src/user/user.service.ts

@@ -28,6 +28,14 @@ export class UserService {
     private readonly roomModel: Model<Room>,
   ) {}
 
+  async getUsersInGroup(groupId: number) {
+    const users = await this.userRepository.find({
+      where: { group: { id: groupId } },
+      relations: ['userInfo', 'group'],
+    });
+    return users;
+  }
+
   async getGroupUsers(userId: number) {
     const user = await this.userRepository.findOne({
       where: { id: userId },