function appendFile
Usage
import { appendFile } from "node:fs/promises";
Asynchronously append data to a file, creating the file if it does not yet
exist. data can be a string or a Buffer.
If options is a string, then it specifies the encoding.
The mode option only affects the newly created file. See fs.open() for more details.
The path may be specified as a FileHandle that has been opened
for appending (using fsPromises.open()).
optional
options: (ObjectEncodingOptions & FlagAndOpenMode & { flush?: boolean | undefined; }) | BufferEncoding | null