ssh: Allow `ssh -F ssh_config` (#25619)

- Closes https://github.com/zed-industries/zed/issues/22818

Usage: `ssh -F ssh_config user@host.tld`

```
-F configfile
    Specifies an alternative per-user configuration file. If a configuration file
    is given on the command line, the system-wide configuration file
    (/etc/ssh/ssh_config) will be ignored. The default for the per-user
    configuration file is ~/.ssh/config. If set to “none”, no configuration files
    will be read.
```

Release Notes:

- ssh: Added support for specifying ssh_config files (`ssh -F
ssh_config`) in connection string