fix(jsonschema): sets default values defined in the schema

When we moved to validate `jsonschemas` on the fly instead of
using the pre-compiled validation code, we regressed the existing
implementation by not realizing that the validation isn't setting
defaults anymore. In order to solve the issue, we referred to the
following link,

https://python-jsonschema.readthedocs.io/en/stable/faq/#why-doesn-t-my-schema-s-default-property-set-the-default-on-my-instance

Since we are using the draft07 of JSONSchema, we referred to the
article and updated the code to define a default validator by
extending the Draft7Validator class to set defaults.

We now use this default validator instead of the `jsonschema.validate` method.

riocli/jsonschema/validate.py

@@ -16,8 +16,7 @@
 from pathlib import Path
 
 import yaml
-
-import jsonschema
+from jsonschema import validators, Draft7Validator
 
 
 @lru_cache(maxsize=None)
@@ -30,8 +29,33 @@ def load_schema(resource: str) -> dict:
         return yaml.safe_load(f)
 
 
+def extend_with_default(validator_class):
+    validate_properties = validator_class.VALIDATORS["properties"]
+
+    def set_defaults(validator, properties, instance, schema):
+        for p, sub_schema in properties.items():
+            if "default" in sub_schema:
+                if isinstance(instance, dict):
+                    instance.setdefault(p, sub_schema["default"])
+                if isinstance(instance, list):
+                    for i in instance:
+                        i.setdefault(p, sub_schema["default"])
+
+        for error in validate_properties(
+                validator, properties, instance, schema,
+        ):
+            yield error
+
+    return validators.extend(
+        validator_class, {"properties": set_defaults},
+    )
+
+
+DefaultValidator = extend_with_default(Draft7Validator)
+
+
 def validate_manifest(instance, schema) -> None:
     """
     Validates a manifest against a JSON schema.
     """
-    jsonschema.validate(instance, schema)
+    DefaultValidator(schema).validate(instance)