Assistant: support for uploading multiple files

[akanshaaa19]

Is your feature request related to a problem? Please describe.
Right now when creating an assistant we can only upload one file at a time, which is not convenient as sometimes there can be more

Describe the solution you'd like
Add support for uploading multiple files at once

[Vikaspal8923]

I think we need some change in both frontend and backend to fix this issue .we have to modify the file input field to allow multiple file selection and have to update API to accept and process multiple files in a single request. we can use array to store multiple file in frontend and then send that array to backend for further process.