Stabilize GroupsController and Address Flaky Test Issues

[aaronlippold]

Description:

The CI job for the GroupsController has encountered the following issues:

Database Deadlock:

Deadlocks were observed in the GroupUsers table during deletion operations.
Likely caused by concurrent transactions acquiring locks in different orders.

Flaky Test in GroupsController:

The test should stop regular users and others from updating a group failed intermittently.
This might occur due to reliance on shared database state and improper isolation.

Duplicate Key Violation:

A duplicate key error was observed on the Users_email_key constraint.
Indicates that the database state is not properly reset between tests.

Proposed Solutions:

1. Fix Deadlocks:
   Ensure consistent locking order and use explicit transactions.
   Example:

await this.databaseService.sequelize.transaction(async (transaction) => {
  await this.groupUserModel.destroy({ where: { groupId }, transaction });
});

2. Improve Test Isolation:
   Reset the database state properly in beforeEach() hooks.
   Example:

beforeEach(async () => {
  await databaseService.cleanAll();
  basicUser = await usersService.create(CREATE_USER_DTO_TEST_OBJ);
});

3. Handle Duplicate Key Errors:
   Use UPSERT or check for existing records before insertion.
   Example:

await this.userModel.upsert({ email: 'example@example.com' }, { conflictFields: ['email'] });

4. Improve Test Assertions:

Ensure the ForbiddenError is reliably thrown and validated.
Example:

await expect(
  groupsController.update({ user: basicUser }, privateGroup.id, UPDATE_GROUP)
).rejects.toThrow('You do not have permission to update this group');

Additional Context:

The failure logs can be found here.