User module | Login Feature

### User story

- As a user, you should be able to log into the application using a valid email and password.
- If the email or password is incorrect, the application will display an error message indicating that the login credentials are invalid. If the email is invalid, the error message will be "Invalid email address," and if the password is invalid, the error message will be "Invalid password."

### DAO:
UserDAO

- [x] findUserByEmail()

### Service:

- [x] logInUser()

### Service Tests:

- [x] testLogInUser()
- [x] testLogInFail()

### Login Flow

```mermaid
flowchart TD
A[Start]
B[Display Login Form]
C[User Enters Credentials]
D[Validate Credentials]
E{Validation Successful?}
F[Generate Token]
G[Login Successful]
H[Display Error Message]
I[End]
A --> B
B --> C
C --> D
D --> E
E -- Yes --> F
F --> G
E -- No --> H
H --> B
G --> I

```