Add docs to Feature.groovy

This might help us to think of everything when adding more features.

Author: schnatterer

docs/developers.md

@@ -589,7 +589,7 @@ That's why we need to initialize our local cluster with some netpols for everyth
 After the cluster is initialized and before GOP is applied, do the following:
 
 ```bash
-# When using harbor, do teh same for namespace harbor
+# When using harbor, do the same for namespace harbor
 k apply -f- <<EOF
 kind: NetworkPolicy
 apiVersion: networking.k8s.io/v1

src/main/groovy/com/cloudogu/gitops/Feature.groovy

@@ -2,6 +2,31 @@ package com.cloudogu.gitops
 
 import groovy.util.logging.Slf4j
 
+/**
+ * A single tool to be deployed by GOP.
+ * 
+ * Typically, this is a helm chart (see {@link com.cloudogu.gitops.features.deployment.DeploymentStrategy} and 
+ * {@code downloadHelmCharts.sh}) with its own section in the config
+ * (see {@link com.cloudogu.gitops.config.schema.Schema#features}).<br/><br/>
+ * 
+ * In the config, features typically set their default helm chart coordinates and provide options to
+ * <ul>
+ *   <li>configure images</li>
+ *   <li>overwrite default helm values</li>
+ * </ul><br/>
+ * 
+ * In addition to their own config, features react to several generic GOP config options.<br/>
+ * Here are some typical examples:
+ * <ul>
+ *   <li>Mirror the Helm Chart: {@link com.cloudogu.gitops.config.schema.Schema.ApplicationSchema#mirrorRepos} see {@link com.cloudogu.gitops.utils.AirGappedUtils#mirrorHelmRepoToGit(java.util.Map)} </li>
+ *   <li>Create Image Pull Secrets: {@link com.cloudogu.gitops.config.schema.Schema.RegistrySchema#createImagePullSecrets} see {@link FeatureWithImage}</li>
+ *   <li>Install with Network Policies: {@link com.cloudogu.gitops.config.schema.Schema.ApplicationSchema#netpols}</li>
+ *   <li>Install with Resource requests + limits: {@link com.cloudogu.gitops.config.schema.Schema.ApplicationSchema#podResources}</li>
+ *   <li>Install without CRDs: {@link com.cloudogu.gitops.config.schema.Schema.ApplicationSchema#skipCrds}</li>
+ *   <li>For apps with UI: Setting {@link com.cloudogu.gitops.config.schema.Schema.ApplicationSchema#username} and {@link com.cloudogu.gitops.config.schema.Schema.ApplicationSchema#password}</li>
+ * </ul>
+ */
+
 @Slf4j
 abstract class Feature {