fix(model): change configuration from struct to string (#72)

Because

- We can safely use string to replace `google.protobuf.Struct` for now, as `google.protobuf.FieldMask` just doesn’t work with `google.protobuf.Struct` at all. Another thing is that we store a JSON struct type in the database as `JSONB` and its GORM mapping is `datatypes.JSON` which is nothing but `[]byte` (i.e., a string).

This commit

- update configuration in model and model_instance from ` google.protobuf.Struct` to string

instill/connector/v1alpha/connector_definition.proto

@@ -209,7 +209,9 @@ message GetSourceConnectorDefinitionRequest {
       type : "api.instill.tech/SourceConnectorDefinition"
     },
     (grpc.gateway.protoc_gen_openapiv2.options.openapiv2_field) = {
-      field_configuration : {path_param_name : "source_connector_definition.name"}
+      field_configuration : {
+        path_param_name : "source_connector_definition.name"
+      }
     }
   ];
   // SourceConnectorDefinition resource view (default is DEFINITION_VIEW_BASIC)

instill/model/v1alpha/model.proto

@@ -48,10 +48,9 @@ message Model {
     (google.api.field_behavior) = IMMUTABLE,
     (google.api.resource_reference).type = "api.instill.tech/ModelDefinition"
   ];
-  // Model configuration represents the configuration JSON object that has been
+  // Model configuration represents the configuration JSON string that has been
   // validated using the `model_spec` JSON schema of a ModelDefinition
-  google.protobuf.Struct configuration = 6
-      [ (google.api.field_behavior) = IMMUTABLE ];
+  string configuration = 6 [ (google.api.field_behavior) = IMMUTABLE ];
   // Model visibility including public or private
   Visibility visibility = 7 [ (google.api.field_behavior) = OUTPUT_ONLY ];
   // Model owner
@@ -122,11 +121,10 @@ message ModelInstance {
     (google.api.field_behavior) = OUTPUT_ONLY,
     (google.api.resource_reference).type = "api.instill.tech/ModelDefinition"
   ];
-  // Model instance configuration represents the JSON configuration that has
-  // been validated using the `model_instance_spec` JSON schema of a
+  // Model instance configuration represents the configuration JSON string that
+  // has been validated using the `model_instance_spec` JSON schema of a
   // ModelDefinition
-  google.protobuf.Struct configuration = 7
-      [ (google.api.field_behavior) = OUTPUT_ONLY ];
+  string configuration = 7 [ (google.api.field_behavior) = OUTPUT_ONLY ];
   // Model instance create time
   google.protobuf.Timestamp create_time = 8
       [ (google.api.field_behavior) = OUTPUT_ONLY ];