Add feature state templates (#3680)

* Add feature state template

* tweak css

* change wording

* apply wording changes to alpha and beta

* tweak dialog css

* tweak code highlighting

* tweak dialog style

* set for_k8s_version default

* tweak dialog ul

* make init containers 1.5 beta for now

* set default dialog width

* revert a:visited color

* force code style

* simplify copy for alpha, beta, stable

* tweak code style

* fix beta dialog title

* fix dialog link a code

* remaining tweaks

* set a:visited color

* Address Steve's feedback

* rename dialog.md to feature-dialog.md

* remove bold from additional feature state text

_includes/feature-state-stable.md

@@ -0,0 +1,10 @@
+{% assign dialog_title = "stable" %}
+{% capture dialog_content %}
+This feature is *stable*, meaning:
+
+* The version name is vX where X is an integer.
+* Stable versions of features will appear in released software for many subsequent versions.
+
+{% endcapture %}
+
+**FEATURE STATE:** `Kubernetes {{ for_k8s_version | default: page.version }}` {% include feature-dialog.md %}