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-beta.md

@@ -0,0 +1,14 @@
+{% assign dialog_title = "beta" %}
+{% capture dialog_content %}
+This feature is currently in a *beta* state, meaning:
+
+* The version names contain beta (e.g. v2beta3).
+* Code is well tested. Enabling the feature is considered safe. Enabled by default.
+* Support for the overall feature will not be dropped, though details may change.
+* The schema and/or semantics of objects may change in incompatible ways in a subsequent beta or stable release. When this happens, we will provide instructions for migrating to the next version. This may require deleting, editing, and re-creating API objects. The editing process may require some thought. This may require downtime for applications that rely on the feature.
+* Recommended for only non-business-critical uses because of potential for incompatible changes in subsequent releases. If you have multiple clusters that can be upgraded independently, you may be able to relax this restriction.
+* **Please do try our beta features and give feedback on them! After they exit beta, it may not be practical for us to make more changes.**
+
+{% endcapture %}
+
+**FEATURE STATE:** `Kubernetes {{ for_k8s_version | default: page.version }}` {% include feature-dialog.md %}