[BE] : Add comment function

src/service/firestore/ecosystem/addComment.ts

+import firebase from "firebase";
+import { getEnv } from "../../../helpers/getEnv";
+export const addComments = async (
+  threadId: string,
+  comment: string,
+  userId: string
+) => {
+  const db = firebase.firestore();
+  return await db.collection("threads_comments_" + getEnv()).add({
+    threadId: threadId,
+    timestamp: firebase.firestore.FieldValue.serverTimestamp(),
+    content: comment,
+    userId: userId,
+  });
+};