Prevent encoding errors for data files

[dalito]

Some people upload ascii-encoded csv but have unicode or latin-1 characters in the file. These files are then not correctly displayed. Example (deg-symbol in header of right column): https://repository.nfdi4cat.org/file.xhtml?persistentId=hdl:21.11165/4cat/9m3x-9a96/2&version=3.0

Dataverse docs on encoding https://guides.dataverse.org/en/latest/user/tabulardataingest/csv-tsv.html#recognized-data-types-and-formatting
suggests to use utf-8 encoding whenever non-ascii charaters are in the files

This issue is about adding a check for presence of chars > 127 in ascii-encoded files on upload to warn the user about the problem. In principle, the publication of datasets with such errors should be prevented.