Add unknown section validation and throw error when unknown section is located in files.

[MRVermeulenDeltares]

Is your feature request related to a problem? Please describe.
In #622 validation for unknown keys was added.
In this issue it also throws an error when a unknown key is in the files.
This should also be adapted for the sections.

Describe the solution you'd like
When a file contains a unknown section it will throw an error on validation.

Describe alternatives you've considered
Not using files with unknown sections.

Additional context
N.A.