Update docs about service principal authentication in external CI tools

[nilsgstrabo]

Information on how to grant a service principal access to administer a Radix application (https://www.radix.equinor.com/guides/deploy-only/#ad-service-principal-access-token) is outdated. It is no longer a requirement to create an EntraID groups which the SP must be member of. The SP can be added as an administrator directly in the Administrator field in Radix Web Console.