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/ssh/ssh.go

@@ -563,11 +563,16 @@ func GetHostConfig(hostname, username, port string) (HostConfig, error) {
 	}
 
 	idf = ssh_config.Get(hostname, "IdentityFile")
-
-	hostConfig.Host = host
 	if idf != "" {
+		var err error
+		idf, err = identityFileAbsPath(idf)
+		if err != nil {
+			return hostConfig, err
+		}
 		hostConfig.IdentityFile = idf
 	}
+
+	hostConfig.Host = host
 	hostConfig.Port = port
 	hostConfig.User = username
 
@@ -575,3 +580,25 @@ func GetHostConfig(hostname, username, port string) (HostConfig, error) {
 
 	return hostConfig, nil
 }
+
+func identityFileAbsPath(relPath string) (string, error) {
+	var err error
+	var absPath string
+
+	if strings.HasPrefix(relPath, "~/") {
+		systemUser, err := user.Current()
+		if err != nil {
+			return absPath, err
+		}
+		absPath = filepath.Join(systemUser.HomeDir, relPath[2:])
+	} else {
+		absPath, err = filepath.Abs(relPath)
+		if err != nil {
+			return absPath, err
+		}
+	}
+
+	logrus.Debugf("resolved %s to %s to read the ssh identity file", relPath, absPath)
+
+	return absPath, nil
+}