validation: improve warning message for unexpected properties

Change the warning message generated when unexpected properties are
found in the REANA specification during the validation phase to include
the path to the invalidating properties.

Closes reanahub#679.

reana_client/validation/utils.py

@@ -58,15 +58,24 @@ 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",