feat: inherit field for release template inheritance (#606)

* feat: `inherit` field for release template inheritance

Ref https://github.com/helmfile/helmfile/issues/435#issuecomment-1364749414

Signed-off-by: Yusuke Kuoka <ykuoka@gmail.com>

* Fix wording

Signed-off-by: Yusuke Kuoka <ykuoka@gmail.com>

* Comment on releaseWithInheritedTemplate

Signed-off-by: Yusuke Kuoka <ykuoka@gmail.com>

* Update Release Template doc with the new `inherit` feature

Signed-off-by: Yusuke Kuoka <ykuoka@gmail.com>

* Fix a typo in code comment

Signed-off-by: Yusuke Kuoka <ykuoka@gmail.com>

Signed-off-by: Yusuke Kuoka <ykuoka@gmail.com>

test/e2e/template/helmfile/testdata/snapshot/pr_560/output.yaml

@@ -82,7 +82,7 @@ remote> getter dest: values/https_github_com_helmfile_helmfile_git.ref=main
 remote> cached dir: /home/runner/.cache/helmfile/values/https_github_com_helmfile_helmfile_git.ref=main
 skipping missing secrets file matching "git::https://github.com/helmfile/helmfile.git@test/e2e/template/helmfile/testdata/snapshot/pr_560/secrets.yaml?ref=main"
 Templating release=foo, chart=../../charts/raw-0.1.0
-exec: helm template foo ../../charts/raw-0.1.0 --values /tmp/helmfile/foo-values-649697bc75 --debug
+exec: helm template foo ../../charts/raw-0.1.0 --values /tmp/helmfile/foo-values-d459bc67c --debug
 helm> install.go:192: [debug] Original chart version: ""
 helm> 
 helm> install.go:209: [debug] CHART PATH: /home/runner/work/helmfile/helmfile/test/e2e/template/helmfile/testdata/charts/raw-0.1.0
@@ -108,6 +108,6 @@ metadata:
 data:
   foo: FOO
 
-Removed /tmp/helmfile/foo-values-649697bc75
+Removed /tmp/helmfile/foo-values-d459bc67c
 Removed /tmp/helmfile
 changing working directory back to "/home/runner/work/helmfile/helmfile/test/e2e/template/helmfile"

test/e2e/template/helmfile/testdata/snapshot/release_template_inheritance/config.yaml

@@ -0,0 +1,5 @@
+localChartRepoServer:
+  enabled: true
+  port: 18084
+helmfileArgs:
+- template

test/e2e/template/helmfile/testdata/snapshot/release_template_inheritance/input.yaml

@@ -0,0 +1,63 @@
+repositories:
+- name: myrepo
+  url: http://localhost:18084/
+
+templates:
+  base:
+    valuesTemplate:
+    - base: base
+    labels:
+      base: base
+  template1:
+    values:
+    - template1: template1
+    valuesTemplate:
+    - template1Label: "{{` '{{ .Release.Labels.template1 }}' `}}"
+    labels:
+      template1: template1
+    inherit:
+      template: base
+      except:
+      - labels
+  template2:
+    values:
+    - template2: template2
+    valuesTemplate:
+    - inheritedBaseLabel: "{{` '{{ .Release.Labels.base }}' `}}"
+      template2Label: "{{` '{{ .Release.Labels.template2 }}' `}}"
+    labels:
+      template2: template2
+    inherit:
+      template: base
+      except:
+      - valuesTemplate
+
+releases:
+- name: foo1
+  chart: ../../charts/raw-0.1.0
+  inherit:
+    template: template1
+  values:
+  - templates:
+    - |
+      apiVersion: v1
+      kind: ConfigMap
+      metadata:
+        name: {{`{{ .Release.Name }}`}}-1
+        namespace: {{`{{ .Release.Namespace }}`}}
+      data:
+        {{` {{ .Values | toYaml | nindent 2 }} `}}
+- name: foo2
+  chart: ../../charts/raw-0.1.0
+  inherit:
+    template: template2
+  values:
+  - templates:
+    - |
+      apiVersion: v1
+      kind: ConfigMap
+      metadata:
+        name: {{`{{ .Release.Name }}`}}-1
+        namespace: {{`{{ .Release.Namespace }}`}}
+      data:
+        {{` {{ .Values | toYaml | nindent 2 }} `}}

test/e2e/template/helmfile/testdata/snapshot/release_template_inheritance/output.yaml

@@ -0,0 +1,45 @@
+Adding repo myrepo http://localhost:18084/
+"myrepo" has been added to your repositories
+
+Building dependency release=foo1, chart=../../charts/raw-0.1.0
+Building dependency release=foo2, chart=../../charts/raw-0.1.0
+Templating release=foo1, chart=../../charts/raw-0.1.0
+---
+# Source: raw/templates/resources.yaml
+apiVersion: v1
+kind: ConfigMap
+metadata:
+  name: foo1-1
+  namespace: default
+data:
+   
+  base: base
+  template1: template1
+  template1Label: template1
+  templates:
+  - "apiVersion: v1\nkind: ConfigMap\nmetadata:\n  name: {{ .Release.Name }}-1\n  namespace:
+    {{ .Release.Namespace }}\ndata:\n   {{ .Values | toYaml | nindent 2 }} \n"
+
+Templating release=foo2, chart=../../charts/raw-0.1.0
+---
+# Source: raw/templates/resources.yaml
+apiVersion: v1
+kind: ConfigMap
+metadata:
+  name: foo2-1
+  namespace: default
+data:
+   
+  inheritedBaseLabel: base
+  template2: template2
+  template2Label: template2
+  templates:
+  - |-
+    apiVersion: v1
+    kind: ConfigMap
+    metadata:
+      name: {{ .Release.Name }}-1
+      namespace: {{ .Release.Namespace }}
+    data:
+       {{ .Values | toYaml | nindent 2 }}
+