re #29 backend implementation of Google OAuth2 authentication
Includes new user registration.
re #37 add email value to testuser record in init.sql script
Fixed is not able to set lower number of sick day than is already taken
Set utf8 database encoding
Default photo
Handle different or non inputs, unit tests, error messages
Deletion of enums from the database
Re #7551 Connection between database and frontend
Re #7551 Typing errors in init script
Re #7551 Remove taken vacations from api and db
Re #7551 Admin user
Re #7526 Database queries
Re #7385 Initialisation of the database
Re #7386 Implemented APIs endpoints with DTOs