[Bug] Empty cluster drowndown and no executor available even though clusters are added

### Search before asking

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

### Paimon UI version

main

### Compute Engine

Flink

### Minimal reproduce step

1. Bring up a local instance of mysql, paimon and flink
2. Create a cluster connection in paimon webui
3. Try to run a query against that cluster

### What doesn't meet your expectations?

Should be able to select one of the existing clusters to run the query against but the dropdown is empty.

### Anything else?

_No response_

### Are you willing to submit a PR?

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