[BUG] Users created by OIDC ignore the IRIS_NEW_USERS_DEFAULT_GROUP setting

[SilPan]

Describe the bug
There is a setting in .env named IRIS_NEW_USERS_DEFAULT_GROUP, which is described that newly created users are added to that group. It looks like this was built for LDAP and when the OIDC functionality was added, it got overlooked.
It does not happen.

To Reproduce
Steps to reproduce the behavior:

1. Configure OIDC authentication.
2. Set the environment variable IRIS_AUTHENTICATION_CREATE_USER_IF_NOT_EXIST to true.
3. Set the environment variable IRIS_NEW_USERS_DEFAULT_GROUP to a value that corresponds to an existing Group name, like 'Analysts'.
4. Log in as user that will be newly created.
5. Observe to be not part of any Group.
   Expected behavior
   Be part of the Group specified in IRIS_NEW_USERS_DEFAULT_GROUP .

Desktop (please complete the following information):

• Browser Firefox 140.13.0. ESR
• Version v2.4.27

[SilPan]

@dynek describes this issue here: #821 (comment)