refactor: use 'mime' package to determine a file's extension

package.json

@@ -62,6 +62,7 @@
     "formik": "^2.4.6",
     "gravatar-url": "3.1.0",
     "lodash": "4.17.21",
+    "mime": "3",
     "next": "^14.2.4",
     "node-cache": "5.1.2",
     "node-gyp": "9.3.1",
@@ -119,6 +120,7 @@
     "@types/express": "4.17.17",
     "@types/express-session": "1.17.6",
     "@types/lodash": "4.14.191",
+    "@types/mime": "3",
     "@types/node": "20.14.8",
     "@types/node-schedule": "2.1.0",
     "@types/nodemailer": "6.4.7",