Analyse: how to link users between AnsattPorten & Github

### Description

We need to find out how or if it's possible to link existing users registered with Github, to new  AnsattPorten users. 



### Additional Information

- Can we override the authentication source in Gitea?
- If not possible how many users to we have using Github?

### Tasks

_No response_

### Acceptance Criterias

_No response_