feat: add --skip-diff-validation-on-install CLI flag (#2728)

Signed-off-by: Richter <h.richter@sap.com>

docs/cli.md

@@ -161,6 +161,11 @@ To supply the diff functionality Helmfile needs the [helm-diff](https://github.c
 you should be able to simply execute `helm plugin install https://github.com/databus23/helm-diff`. For more details
 please look at their [documentation](https://github.com/databus23/helm-diff#helm-diff-plugin).
 
+#### Notable diff flags
+
+* `--skip-diff-on-install` — skip running `helm diff` entirely for releases that are not yet installed. The release is treated as changed and will be synced on `apply` without showing a diff.
+* `--skip-diff-validation-on-install` — for releases that are not yet installed, pass `--disable-validation` to `helm diff` so the diff is shown without K8s API server validation. Useful when a chart bundles CRDs and CRs together: the CRs would fail API validation before the CRDs are installed. This is the CLI-flag equivalent of the per-release `disableValidationOnInstall` field.
+
 ### doctor
 
 `helmfile doctor` runs `helmfile diff` and asks an OpenAI-compatible LLM to summarize the changes and flag risks

docs/configuration.md

@@ -265,6 +265,7 @@ releases:
     # passes --disable-validation to helm diff plugin, this requires diff plugin >= 3.1.2
     # It is useful when any release contains custom resources for CRDs that is not yet installed onto the cluster.
     # https://github.com/roboll/helmfile/pull/1618
+    # To apply this to all releases without editing each one, use the --skip-diff-validation-on-install CLI flag.
     disableValidationOnInstall: false
     # passes --disable-openapi-validation to helm diff plugin, this requires diff plugin >= 3.1.2
     # It may be helpful to deploy charts with helm api v1 CRDS