docs(test-cli): document --trace mode (#19474)

docs/src/test-cli-js.md

@@ -107,6 +107,8 @@ Complete set of Playwright Test options is available in the [configuration file]
 
 - `--timeout <number>`: Maximum timeout in milliseconds for each test, defaults to 30 seconds. Learn more about [various timeouts](./test-timeouts.md).
 
+- `--trace <mode>`: Force tracing mode, can be `on`, `off`, `on-first-retry`, `retain-on-failure`
+
 - `--ignore-snapshots`: Whether to ignore [snapshots](./test-snapshots.md). Use this when snapshot expectations are known to be different, e.g. running tests on Linux against Windows screenshots.
 
 - `--update-snapshots` or `-u`: Whether to update [snapshots](./test-snapshots.md) with actual results instead of comparing them. Use this when snapshot expectations have changed.