Fail / warn if no spectra files are found

[picciama]

Is your feature request related to a problem? Please describe.

If the folder specified in the config does not contain any files that fit to the given spectra_type argument, the rescoring pipeline simply skips all the processing steps until percolator which leads to an error message that is not immediately clear to the user as the pipeline searches for files that weren't created.

Describe the solution you would like

Fail in case of no files with the specified suffix.
Log output that shows the number of files found

Additional context