Update login scenario test

[NyakudyaA]

Feature description

The tests https://github.com/kartoza/docker-geoserver/blob/develop/scenario_tests/login/docker-compose.yml test the passwords created using env variables. It would also help if we could add an additional test that creates a new user and assigns a password using the rest API and we can test if this works when login in.

curl -v -u admin:myawesomegeoserver -X POST -H "Content-Type: application/xml" -d '<?xml version="1.0" encoding="UTF-8"?><user><userName>userxml</userName><password>passwordxml</password><enabled>true</enabled></user>' http://localhost:8600/geoserver/rest/security/usergroup/users/

Additional context

No response