feat: loosen the type restrictions on attr.Json

Just like `json.Marshal` takes arguments of `any` type, the `attr.Json`
should have similarly loose restrictions on input type.

pkg/attr/attr.go

@@ -142,7 +142,7 @@ func JsonAttr(key string, jsonEl map[string]interface{}) attribute.KeyValue {
 
 // Create an arbitrary attribute with value marshalled to json.
 // In case of marshalling error, it is returned in place of value.
-func Json[M json.Marshaler](key string, val M) attribute.KeyValue {
+func Json(key string, val any) attribute.KeyValue {
 	data, err := json.Marshal(val)
 	if err != nil {
 		return attribute.KeyValue{Key: attribute.Key(key), Value: attribute.StringValue(err.Error())}