feat: Option to pass apiVersions to helm diff and helm template (#1046)

This makes it possible to pass the API Capabilities to helmfile when executing a task that does not render against an actual cluster (diff, template, apply).

Resolves #1014

README.md

@@ -95,7 +95,6 @@ helmDefaults:
   # limit the maximum number of revisions saved per release. Use 0 for no limit (default 10)
   historyMax: 10
 
-
 # The desired states of Helm releases.
 #
 # Helmfile runs various helm commands to converge the current state in the live cluster to the desired state defined here.
@@ -267,6 +266,18 @@ bases:
 - environments.yaml
 - defaults.yaml
 - templates.yaml
+
+#
+# Advanced Configuration: API Capabilities
+#
+# Some helmfile tasks render releases locally without querying an actual cluster (diff, apply, template),
+# and in this case `.Capabilities.APIVersions` cannot be populated.
+# When a chart queries for a specific CRD, this can lead to unexpected results.
+# 
+# Configure a fixed list of api versions to pass to helm via the --api-versions flag:
+apiVersions:
+- example/v1
+
 ```
 
 ## Templating