make the openshift / local deployment easier to customize

[lucamaf]

At the moment the deployment script deploys kafka and other component from predefined versions and there is for example no way to attach Drogue to an already exisiting kafka installation.
This is an issue because in terms of CRD on K8S it could conflict with the currently installed strimzi CRD
Same goes for keycloak or grafana

[ctron]

It is possible to do that. You can choose between using an existing Kafka installation elsewhere, deploy Strimzi during the default installation, or re-use an existing Strimzi installation:

https://github.com/drogue-iot/drogue-cloud-helm-charts/blob/0c947c10afa82c462a5da15861e3b221fbd003c4/charts/drogue-cloud-core/values.yaml#L314-L316

However, we might not have documented that well enough (at all). Same goes for Keycloak and Grafana.

With Keycloak the issue however is, that Keycloak CRDs don't live up to their API versioning. So it just breaks between releases. Which means you need to disable the Keycloak installation we provide and do your own. Which also works:

https://github.com/drogue-iot/drogue-cloud-helm-charts/blob/0c947c10afa82c462a5da15861e3b221fbd003c4/charts/drogue-cloud-core/values.yaml#L221-L222