Added login functionality, fixed a typo in auth_routes.py and fixed services.py typos

[TemplarBrotherKnight]

📝 Description

I added login functionality and tested it with postman.

🔗 Linked Issue (Required)

Closes: #11

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🧪 Testing

I ran the server with "flask run" and then tested the "/login" route with several tests.

1. I registered a new user so I know his information.
2. I tried logging in with a username and a password and then with an email and a password and got 200 with the appropriate text.
3. I tried logging in with an empty password and no password key declared at all, no username and no email address and got the same result 400, with the appropriate text.
4. I tried logging in with the correct username/email and wrong password and got 401 with the appropriate text.

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🎓 Learning Reflection

Have more skill. The problem was a skill issue.

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📸 Screenshots / Logs (if applicable)

[karastoyanov]

login route is correct, but we can optimize it a bit

[karastoyanov]

LGTM