[Expl.] Technical user with connector registration connection - asynchron users

[jjeroch]

Interim solution of #843 to be explored and longterm solution to be defined

[MaximilianHauer]

@ntruchsess i assigned this to you i assume there is no point in adding more information currently lets have a short talk as soon as you start the exploration and then see what the result is.

Description:
The current backend implementation for the endpoints /api/administration/Connectors and /api/administration/Connectors/managed prohibits the registration of connectors if the linked technical user is in the "PENDING" status. This restriction needs to be revised to allow the registration of connectors even when the technical user has a "PENDING" status. It is important to note that this change is an interim solution to address immediate needs. The development of a long-term solution is underway but not yet complete.

Acceptance Criteria:

Update the backend logic for /api/administration/Connectors to allow the registration of connectors with technical users in the "PENDING" status.
Update the backend logic for /api/administration/Connectors/managed to allow the registration of connectors with technical users in the "PENDING" status.
Ensure that the registration process remains secure and compliant with existing protocols.
Validate that once registered, the connectors function as expected without any issues related to the technical user's "PENDING" status.
Update any relevant unit tests and add new ones if necessary to cover this new logic.
Perform thorough testing to ensure no unintended side effects result from this change.
Update documentation to reflect this interim change in the registration process.
Ensure the changes are backward compatible to avoid any disruptions to existing users.
Note: This change is a temporary measure until the long-term solution is developed and deployed. We need to ensure that the quality and security of the system are not compromised during this interim period. Exploration for the longterm solution: #844