fix(slack): add instillSecret: true to token field (#126)

Because

- We want the token is secret.

This commit

- make the token secret

pkg/connector/slack/v0/config/definition.json

@@ -22,13 +22,14 @@
             "instillAcceptFormats": [
               "string"
             ],
-            "instillCredentialField": false,
+            "instillSecret": true,
             "instillUIOrder": 0,
             "title": "token",
             "type": "string"
           }
         },
-        "required": [],
+        "required": ["token"],
+        "instillEditOnNodeFields": ["token"],
         "title": "Slack Connection",
         "type": "object"
       }

pkg/connector/slack/v0/taskFunctions.go

@@ -77,6 +77,10 @@ func (e *execution) readMessage(in *structpb.Struct) (*structpb.Struct, error) {
 	}
 	wg.Wait()
 
+	if readTaskResp.Conversations == nil {
+		readTaskResp.Conversations = []Conversation{}
+	}
+
 	out, err := base.ConvertToStructpb(readTaskResp)
 	if err != nil {
 		return nil, err