validation: improve warning message for unexpected properties

Change validation.utils so that the warning message for additional unexpected properties
also includes the path in reana.yaml where the unexpected property was found.

Closes reanahub#679.

reana_client/validation/utils.py

@@ -58,15 +58,21 @@ def validate_reana_spec(
                 msg_type="warning",
                 indented=True,
             )
-        for warning_key, warning_value in validation_warnings.items():
+        for warning_key, warning_values in validation_warnings.items():
             if warning_key == "additional_properties":
                 # warning_values is a list of unexpected properties
+                messages = [
+                    f"'{value['property']}' (at {value['path']})"
+                    for value in warning_values
+                ]
                 message = (
                     f"Unexpected properties found in REANA specification file: "
-                    f"{', '.join(warning_value)}"
+                    f"{', '.join(messages)}."
                 )
             else:
-                message = warning_value
+                # warning_values is a list of dictionaries with 'message' and 'path'
+                messages = [f"{value['message']} (at {value['path']})" for value in warning_values]
+                message = f"{'; '.join(messages)}."
             display_message(
                 message,
                 msg_type="warning",