Add endpoint to retrieve posts by tag with validation

routes/post.js

@@ -95,6 +95,18 @@ DB.getDB.then((DB) => {
         return res.json(posts);
     });
 
+    router.get("/tag/:tag", async (req, res) => {
+        const profileid = getProfileId(req);
+        const tag = req.params.tag;
+        if(!tag) {
+            return res.json({
+                status: "Tag is required",
+            });
+        }
+        let posts = await DB.getPostsByTag(tag, profileid);
+        return res.json(posts);
+    });
+
     router.get("/usr/:id", async (req, res) => {
         const profileId = req.params.id;
         const viewerProdileId = getProfileId(req);