Add default user moss and assign default roles to builtin users

[kulmann]

This PR adds a new default user "Maurice Moss" with credentials moss:vista. It also assigns the default user role to einstein, marie und richard and the default admin role to the new moss user.

[update-docs]

Thanks for opening this pull request! The maintainers of this repository would appreciate it if you would create a changelog item based on your changes.

[ownclouders]

Here is an overview of what got changed by this pull request:

Complexity increasing per file
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- pkg/service/v0/service.go  3
         

See the complete overview on Codacy

[sonarqubecloud]

Kudos, SonarCloud Quality Gate passed!

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