make linux server allow rsync/scp/sftp but not a terminal login

Set the users' shell to rssh. From the manpage:

rssh - restricted secure shell allowing only scp and/or sftp

If you only need to allow rsync, the developers of rsync provide the rrsync script to solve your problem. It is available from here: http://ftp.samba.org/pub/unpacked/rsync/support/rrsync

You just need to add something like this to your .authorized_keys file. This example allows read only (-ro) access to /some/directory/:

command="/path/to/rrsync -ro /some/directory/",no-agent-forwarding,no-port-forwarding,no-pty,no-user-rc,no-X11-forwarding ssh-rsa AAA...

A more throughout explanation and example is available here: https://www.guyrutenberg.com/2014/01/14/restricting-ssh-access-to-rsync/

Update: This is NOT SECURE for write access until this bug is fixed: https://bugzilla.samba.org/show_bug.cgi?id=11879

As long as this bug persists, please only use rrsync in read only mode (-ro).