Updates for MFA

If you're updating this, would you mind also making a change to the settings for handling MFA? These were based on the combination of some discussion with Alliance support and also the following: https://docs.alliancecan.ca/wiki/Multifactor_authentication#Configuring_your_SSH_client_to_only_ask_every_so_often

* Add the following to `.ssh/config` such that MFA is only asked after a period of time rather than each time `ssh`/`sshfs` is called:
```
Host HOSTNAME
ControlPath ~/.ssh/cm-%r@%h:%p
ControlMaster auto
ControlPersist 10m # Can change this to 0 to only ask once
```

* Update `sshfs` with the following options (removes ServerAliveCount and updates ServerAliveInterval):

```
reconnect,ServerAliveInterval=0,Compression=no,follow_symlinks
```

The second point was at least working on a cloud instance I was testing this out on. To that end, the second point is more just to let the mount persist, else `sshfs` will always ask about MFA (and doesn't actually take config AFAIK into consideration).

Note these were all on Linux distros, so not sure of the equivalent for Windows.

_Originally posted by @kaitj in https://github.com/khanlab/wiki/issues/15#issuecomment-1799286355_

Start with the Alliance MFA documentation linked in the issue, then find the wiki's current SSH and sshfs instructions. Update the Linux guidance to cover the .ssh/config ControlMaster settings and the listed sshfs options, and clarify whether Windows equivalents are supported or out of scope.

Written by the indexing model from the issue text.