Use redirect URL in share link if env variable set

[cesnietor]

needs: minio/minio#19683
fixes: #3331

Uses MINIO_BROWSER_REDIRECT_URL to generate the share URL link if it's set.

• Includes unittests

Test Steps with Ngnix

Assuming we are exposing the console under http://localhost:8000/console/subpath/

1. Build MinIO with this change with this branch of console
2. Start MinIO for a given Subpath

CI=true;MINIO_BROWSER_REDIRECT_URL=http://localhost:8000/console/subpath/;MINIO_SERVER_URL=http://localhost:9000 minio --console-address ":9090"

3. Start nginx with the following configuraiton

events { worker_connections 1024; }

http {

server {
    listen 8000;

    location /console/subpath/ {
        rewrite   ^/console/subpath/(.*) /$1 break;
        proxy_pass http://localhost:9090;
        
        proxy_http_version 1.1;
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection "Upgrade";
        proxy_set_header Host $host;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header X-Forwarded-Proto $scheme;
        
        # This allows WebSocket connections
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection "upgrade";
    }
}
}

with the command

nginx -c /PATH/TO/nginx.conf -g "daemon off;"

4. Go to bucket(create if needed), e.g. http://localhost:8000/console/subpath/browser/bucket1
5. Click on a file and click Share
6. URL generated should contain the Subpath