Draft: Set static test user/pw in cypress test

Previously, this test would add a user and add it to a group, and check to see if the user shows up in the user list. The userid was a randomized string.

To test keycloak integration within the various apps, I will need a static username/pw to log in as. Since this test already creates a user and adds it to a group, all I needed on top of this was to set a password on it and make the username a static string.

This script will continue to use randomized userIDs unless a variable cypress_static_testuser is passed to it, in which case it uses the static username testuser.

Related to https://repo1.dso.mil/platform-one/big-bang/bigbang/-/issues/1087