Piet van der Meulen

add readAnyDatabase and stackitAdmin roles for MongoDB users

3

## Description Adding additional roles for MongoDB users. Taken from the [API Docs](https://docs.api.stackit.cloud/documentation/mongodb-flex-service/version/v2#tag/user/paths/~1v2~1projects~1%7BprojectId%7D~1regions~1%7Bregion%7D~1instances~1%7BinstanceId%7D~1users/post). ## Checklist - [ ] ~Issue was linked above~ - [x] Code format was applied: `make fmt`...