fix(sct_config): remove special characters from user_perfix

remove any special characters from `user_prefix`, since later
it will be used as a part of the instance names and some
platfrom don't support special characters in the instance
names (docker, AWS and such)

Fixes: #8919

sdcm/sct_config.py

@@ -1995,6 +1995,10 @@ def __init__(self):  # noqa: PLR0912, PLR0914, PLR0915
             prefix_max_len -= 3
         self['user_prefix'] = user_prefix[:prefix_max_len]
 
+        # remove any special characters from user_prefix, since later it will be used as a part of the instance names
+        # and some platfrom don't support special characters in the instance names (docker, AWS and such)
+        self['user_prefix'] = re.sub(r"[^a-zA-Z0-9-]", "-", self['user_prefix'])
+
         # 11) validate that supported instance_provision selected
         if self.get('instance_provision') not in ['spot', 'on_demand', 'spot_fleet', 'spot_low_price']:
             raise ValueError(f"Selected instance_provision type '{self.get('instance_provision')}' is not supported!")