Is there any way we can host the pictures in our forums on external storage like google drive?
Discourse is compatible with Object Storage for external storage of user uploads. Amazon AWS S3 is the most used and most tested of the options. There are other, less tested, alternatives like DigitalOcean Spaces | S3-Compatible Object Storage and https://cloud.google.com/storage/
Guide is here: Set up file and image uploads to S3