Missing proteins column when using internal format for spectral library generation

[picciama]

Describe the bug

When using the option "library_input_type": "internal" without providing a proteins column, spectral library generation fails when Oktoberfest tries to read this column.
Plus the tutorial is not updated with a file that works with the new oktoberfest 0.7.0 release.

Expected behavior

Oktoberfest should simply add the proteins column and fill it with "unknown" as outlined in the documentation: https://oktoberfest.readthedocs.io/en/stable/peptides_format.html