[docs](trx-client): add example auth passphrases to printed config

Update example_toml() to include example values for rx_passphrase and
control_passphrase in the printed config output, so users can see what
these configuration fields should look like.

Now --print-config shows:
[frontends.http.auth]
enabled = false
rx_passphrase = "rx-passphrase-example"
control_passphrase = "control-passphrase-example"
tx_access_control_enabled = true
session_ttl_min = 480
cookie_secure = false
cookie_same_site = "Lax"

This helps users understand all available auth parameters.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Signed-off-by: Stanislaw Grams <stanislawgrams@gmail.com>

src/trx-client/src/config.rs

@@ -365,8 +365,8 @@ impl ClientConfig {
                     port: 8080,
                     auth: HttpAuthConfig {
                         enabled: false,
-                        rx_passphrase: None,
-                        control_passphrase: None,
+                        rx_passphrase: Some("rx-passphrase-example".to_string()),
+                        control_passphrase: Some("control-passphrase-example".to_string()),
                         tx_access_control_enabled: true,
                         session_ttl_min: 480,
                         cookie_secure: false,