[Heartbeat] Improve the error message for synthetics browser monitor timeout

**Describe the enhancement:**

When the browser monitor script gets timeout or run indefinitely, Once the monitor timeout is done (max 15 minutes), the synthetics browser monitor Node.js process gets killed which results in generic error message like
```
journey did not finish executing, 1 steps ran (attempt: 2): error executing step: command '/tmp/elastic-synthetics-unzip-1555474065/node_modules/.bin/elastic-synthetics /tmp/elastic-synthetics-unzip-1555474065 --playwright-options { REDACTED } --screenshots off --params { REDACTED } --outfd 3' did not exit before extended timeout: 15m30s
```

**Describe a specific use case for the enhancement or feature:**

Improve the error message here suggesting the users to either fix the script or split the tests in to smaller tests.