[Doc] Stateful functions don't work in standalone mode since PIP-117

### Search before asking

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

### What issue do you find in Pulsar docs?

Since the simplifications done with[ PIP-117](https://github.com/apache/pulsar/issues/13302), it is no longer possible to use stateful functions in standalone mode.

It seems the only way out is to run the old setup with Zookeeper:

`PULSAR_STANDALONE_USE_ZOOKEEPER=1 bin/pulsar standalone`

This is however not documented, not here: https://pulsar.apache.org/docs/4.0.x/getting-started-standalone/ and not there: https://pulsar.apache.org/docs/4.0.x/functions-worker-stateful/. This makes life difficult for Pulsar newcomers.

### What is your suggestion?

My proposal would be to mention the need for `PULSAR_STANDALONE_USE_ZOOKEEPER=1` in standalone mode in section https://pulsar.apache.org/docs/4.0.x/functions-worker-stateful/.

However, the perfect solution would be to always support stateful functions by just running `bin/pulsar standalone` ... but that's beyond documentation.

### Any reference?

[PIP-117](https://github.com/apache/pulsar/issues/13302)

### Are you willing to submit a PR?

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

Start with the Pulsar 4.0.x functions-worker-stateful documentation and compare it with the getting-started-standalone page. Document that stateful functions in standalone mode require PULSAR_STANDALONE_USE_ZOOKEEPER=1, and verify that the prerequisite is clearly described for newcomers.

Written by the indexing model from the issue text.