feat(docs): Reference documentation (#650)

* WIP * ~

Author: fhennig

docs/modules/kafka/pages/config_properties.adoc

@@ -1,5 +1,8 @@
+= Command line parameters
 
-=== product-config
+This operator accepts the following command line parameters:
+
+== product-config
 
 *Default value*: `/etc/stackable/kafka-operator/config-spec/properties.yaml`
 
@@ -12,7 +15,7 @@
 stackable-kafka-operator run --product-config /foo/bar/properties.yaml
 ----
 
-=== watch-namespace
+== watch-namespace
 
 *Default value*: All namespaces
 

docs/modules/kafka/pages/configuration.adoc

@@ -0,0 +1,3 @@
+= CRD Reference
+
+Find all CRD reference for the Stackable Operator for Apache Kafka at: {crd-docs-base-url}/kafka-operator/{crd-docs-version}.

docs/modules/kafka/pages/commandline_args.adoc renamed to docs/modules/kafka/pages/reference/commandline-parameters.adoc

@@ -1,5 +1,8 @@
+= Environment variables
 
-=== PRODUCT_CONFIG
+This operator accepts the following environment variables:
+
+== PRODUCT_CONFIG
 
 *Default value*: `/etc/stackable/kafka-operator/config-spec/properties.yaml`
 
@@ -25,7 +28,7 @@ docker run \
  docker.stackable.tech/stackable/kafka-operator:latest
 ----
 
-=== WATCH_NAMESPACE
+== WATCH_NAMESPACE
 
 *Default value*: All namespaces
 

docs/modules/kafka/pages/reference/crds.adoc

@@ -0,0 +1,7 @@
+= Reference
+
+Consult the reference documentation section to find exhaustive information on:
+
+* Descriptions and default values of all properties in the CRDs used by this operator in the xref:reference/crds.adoc[].
+* The properties in the xref:reference/discovery.adoc[].
+* The xref:reference/commandline-parameters.adoc[] and xref:reference/environment-variables.adoc[] accepted by the operator.

docs/modules/kafka/pages/usage-guide/discovery.adoc renamed to docs/modules/kafka/pages/reference/discovery.adoc

@@ -1,11 +1,9 @@
 * xref:kafka:getting_started/index.adoc[]
 ** xref:kafka:getting_started/installation.adoc[]
 ** xref:kafka:getting_started/first_steps.adoc[]
-* xref:kafka:configuration.adoc[]
 * xref:kafka:usage-guide/index.adoc[]
 ** xref:kafka:usage-guide/storage-resources.adoc[]
 ** xref:kafka:usage-guide/security.adoc[]
-** xref:kafka:usage-guide/discovery.adoc[]
 ** xref:kafka:usage-guide/monitoring.adoc[]
 ** xref:kafka:usage-guide/logging.adoc[]
 ** xref:kafka:usage-guide/configuration-environment-overrides.adoc[]
@@ -15,3 +13,10 @@
 *** xref:kafka:usage-guide/operations/pod-disruptions.adoc[]
 *** xref:kafka:usage-guide/operations/graceful-shutdown.adoc[]
 *** xref:kafka:usage-guide/operations/znode-id.adoc[]
+* xref:kafka:reference/index.adoc[]
+** xref:kafka:reference/crds.adoc[]
+*** {crd-docs}/kafka.stackable.tech/kafkacluster/v1alpha1/[KafkaCluster {external-link-icon}^]
+** xref:kafka:reference/discovery.adoc[]
+** xref:kafka:reference/commandline-parameters.adoc[]
+** xref:kafka:reference/environment-variables.adoc[]
+