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-alpha.md

@@ -0,0 +1,13 @@
+{% assign dialog_title = "alpha" %}
+{% capture dialog_content %}
+This feature is currently in a *alpha* state, meaning:
+
+* The version names contain alpha (e.g. v1alpha1).
+* Might be buggy. Enabling the feature may expose bugs. Disabled by default.
+* Support for feature may be dropped at any time without notice.
+* The API may change in incompatible ways in a later software release without notice.
+* Recommended for use only in short-lived testing clusters, due to increased risk of bugs and lack of long-term support.
+
+{% endcapture %}
+
+**FEATURE STATE:** `Kubernetes {{ for_k8s_version | default: page.version }}` {% include feature-dialog.md %}