fix: attempt to include IdentityFile if available

This is part of trying to debug:

    coop-cloud/organising#250

And also part of:

    coop-cloud/docs.coopcloud.tech#27

Where I now try to specify the same logic as `ssh -i <my-key-path>` in
the underlying connection logic. This should help with being more
explicit about what key is being used via the SSH config file.

pkg/upstream/commandconn/connection.go

@@ -2,6 +2,7 @@ package commandconn
 
 import (
 	"context"
+	"fmt"
 	"net"
 	"net/url"
 
@@ -34,9 +35,25 @@ func getConnectionHelper(daemonURL string, sshFlags []string) (*connhelper.Conne
 		if err != nil {
 			return nil, errors.Wrap(err, "ssh host connection is not valid")
 		}
+
 		if err := sshPkg.EnsureHostKey(ctxConnDetails.Host); err != nil {
 			return nil, err
 		}
+
+		hostConfig, err := sshPkg.GetHostConfig(
+			ctxConnDetails.Host,
+			ctxConnDetails.User,
+			ctxConnDetails.Port,
+		)
+		if err != nil {
+			return nil, err
+		}
+		if hostConfig.IdentityFile != "" {
+			msg := "discovered %s as identity file for %s, using for ssh connection"
+			logrus.Debugf(msg, hostConfig.IdentityFile, ctxConnDetails.Host)
+			sshFlags = append(sshFlags, fmt.Sprintf("-o IdentityFile=%s", hostConfig.IdentityFile))
+		}
+
 		return &connhelper.ConnectionHelper{
 			Dialer: func(ctx context.Context, network, addr string) (net.Conn, error) {
 				return New(ctx, "ssh", append(sshFlags, ctxConnDetails.Args("docker", "system", "dial-stdio")...)...)