Improve YAML config parsing

[valosekj]

Raise a custom error when using * as a wildcard character

[valosekj]

Using this config

FILES_LESION:
  - *T2w.nii.gz

And getting the custom error:

ERROR: YAML parsing error in /md1/valosek/results/sci-olomouc/sci-olomouc_2025-07-09/config_lesion_sciseg.yml.
The '*' character is a special character in YAML that denotes an alias or anchor.
To use '*' as a wildcard character, start the line with 'sub' string, e.g.: "sub*T2w.nii.gz"
while scanning an alias
  in "/md1/valosek/results/sci-olomouc/sci-olomouc_2025-07-09/config_lesion_sciseg.yml", line 2, column 5
expected alphabetic or numeric character, but found '.'
  in "/md1/valosek/results/sci-olomouc/sci-olomouc_2025-07-09/config_lesion_sciseg.yml", line 2, column 9