Currently, if a user logs in, all fields listed result in a separate group being created.

This enhancement allows to have combined groups.

The use case is the following:

• A user has one group field for its status, like student or employee
• The user has another group field for it institutional association
• In LEIHS, an admin wants f.e. only employees of a certain institution give access to an inventory pool. This cannot be achieved with the current implementation

To solve this problem, i would like to introduce a new config option called combine_groups. If this boolean is true, the contents of all listed groups is concatenated with , during the login process. This gives a permutation of all possible group combinations which then can be assigned accordingly.