Refactor role request

[eivindkopperud]

WIth https://github.com/NTNUI/membership-system/pull/2617, one no longer needs to make a request to the specific group to figure out which role the user has in the group. This will shortly be added to the JWT claim.

Thus, one needs to base64-decode the access token and parse information about the groups.
Will update the issue once the format has been agreed upon.