[Bug] /status.html endpoint fails when statusFilePath is not set

### Search before asking

- [X] I searched in the [issues](https://github.com/apache/pulsar/issues) and found nothing similar.

### Read release policy

- [X] I understand that unsupported versions don't get bug fixes. I will attempt to reproduce the issue on a supported version of Pulsar client and Pulsar broker.

### Version

any released version

### Minimal reproduce step

1. set statusFilePath to empty in `standalone.conf`
2. start pulsar standalone with `bin/pulsar standalone`
3. go to http://localhost:8080/status.html (or use `curl http://localhost:8080/status.html`)

### What did you expect to see?

that /status.html endpoint returns "OK" when `statusFilePath` is not set and the broker is ready.

### What did you see instead?

The /status.html will always return 404 failure

### Anything else?

There's also invalid default configuration in `standalone.conf`:
https://github.com/apache/pulsar/blob/1f7a79f4c240c8075c217ac417dffa5bc72a4d5f/conf/standalone.conf#L215
This value doesn't make any sense. The default value should be empty (which results in `null`).

### Are you willing to submit a PR?

- [ ] I'm willing to submit a PR!

Start with the statusFilePath setting in conf/standalone.conf and reproduce the issue by running bin/pulsar standalone, then requesting /status.html with curl. Trace the endpoint's handling of an unset status file path; done means the endpoint returns OK when the broker is ready and the default configuration is empty.

Written by the indexing model from the issue text.