To be discussed: Get rid of the differentiation between internal and external users about codeocean

[MrSerth]

With #1698, we further minimised the differences of Internal and External Users. With the recent changes, Internal Users can also experience the very same workflow when finishing an exercise (i.e., finalising it by reaching the full score) as External Users.

Further, we are already using the LTI role instructor to provide teachers with more access permissions. Technically, we are also receiving information about an LTI administrator, but decided against using it automatically for GDPR-related reasons: With the multi-tenancy of CodeOcean, an administrator currently has full access to any data, so that reusing the LTI permission doesn't seem feasible.