Add first draft for using keycloack as idp and delegating auth to it

[hbusul]

I added the keycloak as identity provider and changed the frontend and backend to use it for authorization/authentication instead of implementing our own user system.

For the tests and etc, now it is configurable that you can use the old way of authentication.

[emrdagkusu]

I reviewed the code and try to use a little bit the system. It is functioning well as far as I see. It can be merged.

[emrdagkusu]

I just realized that, we are not actually storing the password of users and we are just creating new users with same password in our MongoDB database. When we create a user the user is being created in Keycloak and after that we are creating a user inside MongoDB database with provided information. There is a problem in here, it is not possible to delete users from our MongoDB database although users can be deleted from Keycloak after giving the permission to users about deleting. We should add functionality to delete users from both MongoDB and Keycloak.