feat: Support Zookeeper discovery type

[pbalaban]

Feature request

Please describe your feature

According to the ApiSix documentation it now supports zookeeper service discovery. I think it would be good to also add the possibility to choose Zookeeper discovery type from the dashboard

Describe the solution you'd like

As far as I can see, the only one change is required here and I would be happy to create a PR for this

Additional context

At the moment this error is raised when zookeeper is added through the ApiSix API

[bzp2010]

Hi, @pbalaban

Thank you for your report, I confirm that this issue exists and it will be fixed in the next release.