[Bug]: Ensure OpenSSH 8.3 or higher is installed

[peterschmidt85]

Steps to reproduce

1. Setup dstack server on a machine with OpenSSH older than 8.3.
2. Create a gateway

Actual behaviour

The server fails to connect to the gateway to set it up.
If the server is restarted, the server hangs while connecting to the gateway.

Expected behaviour

When dstack server is being started, if OpenSSH is older than 8.3, show a warning that
OpenSSH 8.3+ is required.

dstack version

Any

Server logs

No response

Additional information

This happens because dstack relies on ssh's -f option which doesn't work properly with OpenSSH older than 8.3.

From OpenSSH's release notes:

ssh(1): close stdin/out/error when forking after authentication
completes ("ssh -f ...") bz#3137

[r4victor]

I believe the fix was introduced in OpenSSH 8.4 (https://www.openssh.com/txt/release-8.4), so we should check for OpenSSH >= 8.4

[loghijiaha]

Hey @peterschmidt85, I would like to give a hand to fix this bug, May I?

[peterschmidt85]

@loghijiaha That would be amazing! Ping me if you need help or have any questions!