Improve cluster status

[korthout]

Retrieving the cluster status only reports on zeebe currently. However, Operate is now also part of the cluster components that the REST API connects to.

The status should report whether a connection with operate is configured, and if so, whether it is able to connect to it.

This would be useful to simplify the guide to connect to a Self-Managed cluster, because the checking the connection to operate can be done in the same way as checking the connection with zeebe.

This would be useful as this guide is currently quite large and may scare of potential users unnecessarily.